Update 5.20pm: The so-called Islamic State group claimed responsibility for the attack and said the gunman Stephen Paddock was "a soldier" who had converted to Islam months ago, but it provided no evidence to back up the claim.
The FBI has rejected the statement.
Meanwhile, people who knew shooter Stephen Paddock have spoken of their shock. His brother Eric Paddock, outside his home in Orlando, Florida, said: "We (the family) know nothing. If you told me an asteroid fell it would mean the same to me. There's absolutely no sense, no reason he did this.
"He's just a guy who played video poker and took cruises and ate burritos at Taco Bell. There's no political affiliation that we know of. There's no religious affiliation that we know of."
Stephen Paddock was a multi-millionaire property developer, his brother said later.
The Washington Post reports that their father was once on the FBI 10 most wanted list who was an escaped bank robber and was rarely around for his sons.
"I was born on the run," said Eric Paddock.
Neighbours described Stephen Paddock as described as extremely standoffish.
Update - 4.43pm: The death toll from the Las Vegas shooting has risen to at least 58 and 515 people were injured, Nevada Police said.
The FBI have also said that the shooting has no connection with international terrorism.
Guns and ammunition were found at Paddock's "nice clean" home, a Mesquite Police spokesman told reporters.
He said people living either side of the house in a retirement community were evacuated from the area before it was searched as a precaution.
"I believe there were some weapons found and maybe some ammunition," he said, adding that no one was in the house at the time.
Update - 3.55pm: US President Donald Trump has held a press conference after last night's mass shooting in Las Vegas.
The President condemned the incident saying: "It was an act of pure evil".
He went on to say that the FBI are working closely with local police and he offered his condolences to the victims and their families.
He said: "We cannot fathom their pain, we cannot imagine their loss."
He also announced he will be going to Las Vegas on Wednesday to meet with officials and victims.
In a televised address, Mr Trump said the nation is joined together in sadness, shock and grief after the massacre.
Mr Trump said the nation must stay unified.
He added that although "we feel such great anger at the senseless murder of our fellow citizens, it is our love that binds us today and always will".
Mr Trump said flags will be flown at half-mast to honour the victims until sunset on October 6.
The proclamation covers flags at the White House and all public buildings, military posts, naval stations and naval vessels throughout the United States and all territories. It also extends to embassies, military facilities and other sites overseas.
The president said he and first lady Melania Trump are praying for those who have been lost and wounded, and for "the entire nation to find unity and peace".
Update - 3.05pm: Las Vegas police said they have determined that the woman thought to have been the gunman's room-mate is no longer considered a "person of interest" in the inquiry.
Officers do not believe 62-year-old Marilou Danley was involved in the shooting.
Meanwhile, heavily armed police are searching the Nevada retirement-community home of Paddock.
Mesquite Police chief Troy Tanner said officers entered the property where the 64-year-old lived.
He said Ms Danley was not at the house and police saw "no movement" inside the one-storey, three-bedroom home in the Sun City Mesquite retirement community, about 80 miles north of Las Vegas.
Mr Tanner said detectives are at the scene in the resort community, located near the Arizona state line.
Clark County Sheriff Joseph Lombardo said officers believe this was a "lone wolf" attack.
There is no immediate word on the motive for the attack. The US Homeland Security Department said there was no "specific credible threat" involving other public venues in America.
Update - 1.49pm: The Las Vegas Metropolitan Police Department have said that 406 people were taken to hospitals after the shooting in Las Vegas.
The Police Department have identified the suspect as 64-year-old, Stephen Craig Paddock, a white male from Mesquite, Nevada.
They said he opened fire on a crowd of more than 22,000 concert-goers from his hotel room on the 32nd floor of the Mandalay Bay Hotel last night at around 10.08pm.
The force's LVMPD SWAT team responded and after breaking into the hotel room, they found the suspect dead.
The Clark County Fire Department estimated that 406 people were transported to area hospitals and 50 are dead.
The police said: "Among the dead is an LVMPD officer who was off-duty at the time. His name is being withheld pending notification of next of kin.
"There were also two on-duty officers injured, one of whom was upgraded recently from critical to stable condition. The other sustained non-life threatening wounds."
They said it is still "an active investigation" and the FBI is asking for anyone with videos or photos concerning the shooting to call 1-800-CALLFBI or (800) 225-5324.
LVMPD and Clark County Coroner’s Office have set up a hotline for family or friends to report a missing loved one connected to this incident. The hotline is only to take reports on missing people. The number is (866) 535-5654.
They have also opened up a family reunification center at its headquarters at 400 S. Martin L. King Blvd. in Building B.
Update 12.30pm: Minister for Foreign Affairs and Trade, Simon Coveney TD offered his condolences following the shooting incident in Las Vegas.
"I strongly condemn the attack at the Route 91 Harvest country music festival in Las Vegas. This was a savage and brutal attack targeting innocent festival-goers.
"I wish to express my heartfelt condolences and those of the Irish people to the families of the victims, those who were injured and to the people and the authorities of the United States on this tragic day."
Mr Coveney said that by mid-morning there were no indications of Irish citizens being affected.
"As of now, we have no indications to suggest that any Irish citizens have been affected. I am conscious, however, that it will take time before all of the casualties are identified. My Department, through our Consulate General in San Francisco and the Honorary Consulate in Las Vegas, is continuing to monitor the situation.
The department issued a contact number for families in Ireland who have concerns about relatives to ring the consular assistance unit on 01 408 2527.
Update 12.15pm: US President Donald Trump has offered his "warmest condolences" to the victims and families of the shooting in Las Vegas.
My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!— Donald J. Trump (@realDonaldTrump) October 2, 2017
White House spokeswoman Sarah Huckabee Sanders said Mr Trump had been "briefed on the horrific tragedy in Las Vegas".
Ms Sanders said that "we are monitoring the situation closely and offer our full support to state and local officials. All of those affected are in our thoughts and prayers".
Update 11.35am: At least 50 people have been killed and 200 others were injured in a shooting at a concert in Las Vegas.
A Las Vegas resident, named as Stephen Paddock, is suspected of being the man who opened fire on the Route 91 Harvest Festival on the Las Vegas Strip.
The suspect was killed by police on 32nd floor of the Mandalay Bay Hotel and Casino, situated across from the concert.
Sheriff Joseph Lombardo said police have located two vehicles they were searching for and they located the female person of interest, Marilou Danley.
One of the police officers killed worked for the Las Vegas Police Department but was off duty at the time, Lombardo said. Another officer is in a critical condition.
At this time there is in excess of 50 deceased and over 200 injured individuals.— LVMPD (@LVMPD) October 2, 2017
Marilou Danley, 62, had been sought by police after gunfire tore through the crowd at the outdoor event during a set by country music star Jason Aldean.
The dead gunman is also believed to have checked into the hotel as a guest.
Clark County Sheriff Joseph Lombardo said officers confronted Paddock in the hotel.
Update 9.30am: Over 20 people including off-duty police officers have been killed and "well in excess of" 100 people injured in a mass shooting at an outdoor music festival on the Las Vegas Strip, officials said.
"Right now we believe it is 100 plus injured and 20 plus dead," said Joseph Lombardo, the sheriff of the Las Vegas Metropolitan police department. 12 people are in a critical condition.
Some off-duty police officers who were attending the concert are believed to be among the dead.
JUST IN: Bakersfield Police Department says one of its off-duty officers was shot at Mandalay Bay and is being treated in hospital pic.twitter.com/Bndwg1ocSk— NBC News (@NBCNews) October 2, 2017
Las Vegas police later killed a suspect on 32nd floor of a hotel across from the concert, and said they did not believe there were any other attackers.
The suspected shooter's female companion, Marilou Danley, is still at large, according to Las Vegas police. The dead man is believed to be local and his motives are not known.
Joseph Lombardo, the sheriff of the Las Vegas Metropolitan police department, did not name the dead shooter but confirmed he opened fire from the 32nd floor of the Mandalay Bay hotel.
"We are pretty confident that there is no longer a threat," he said.
*WARNING* Video contains graphic scenes which some might find disturbing.
Police are searching for two vehicles, a Hyundai Tuscon and a Chrysler Pacifica Turing.
Marilou Danley is being sought for questioning re the investigation into the active shooter incident. If seen please call 9-1-1! pic.twitter.com/Z83XvcHejH— LVMPD (@LVMPD) October 2, 2017
Update 8.35am: Las Vegas police "do not believe there are any more shooters."
At this time we do not believe there are any more shooters. More information to come shortly from @Sheriff_LVMPD.— LVMPD (@LVMPD) October 2, 2017
Some flights have resumed at the nearby McCarran Airport.
Limited flight activity has resumed at @LASairport. Please monitor flight status with your airline. Expect on going delays.— McCarran Airport (@LASairport) October 2, 2017
The Irish Consulate is advising Irish citizens in the area to follow instructions from local police.
The Consulate is aware of a situation in Las Vegas. Irish citizens are advised to follow instructions from @LVMPD— Irish Consulate W US (@IrelandSanFran) October 2, 2017
Update 8am: At least two people have been killed and 24 others injured, 12 of them critically, in a mass shooting at a music festival on the Las Vegas Strip, hospital officials said.
University Medical Centre spokeswoman Danita Cohen said 26 people had been admitted to the hospital. Of those, at least two had died and 12 were in a critical condition. The rest are being assessed.
One suspect has been shot, Las Vegas police have confirmed.
Confirming that one suspect is down. This is an active investigation. Again, please do not head down to the Strip at this time.— LVMPD (@LVMPD) October 2, 2017
Dozens of patrol vehicles descended on the Strip after authorities received reports of an active gunman near the Route 91 Harvest Festival.
Some officers took cover behind their vehicles while others carrying assault rifles ran into the Mandalay Bay Hotel and Casino.
University Medical Centre spokeswoman Danita Cohen said the hospital was taking in "several" people with gunshot wounds. She did not have any other details.
Authorities shut down part of the Las Vegas Strip and Interstate 15.
Some flights destined for McCarran International Airport were diverted due to the incident.
Witnesses said country singer Jason Aldean was playing near the end of the concert when gunfire rang out.
No further information was immediately known.
A concert-goer said he heard what sounded like fireworks while he was watching Aldean's performance.
Kodiak Yazzi said the music stopped temporarily and then started up again before another round of pops sent the performers ducking for cover and fleeing the stage.
As the 40,000 fans in the crowd began to flee, the 36-year-old took cover and said he saw flashes of light coming from the Mandalay Bay hotel tower high above.
Video shows #LasVegas concert-goers taking cover amid gunfireOctober 2, 2017
The bursts of pops would start and stop for more than five minutes.
He said he saw dozens of ambulances as he ran for safety. He later got a Lyft driver to take him home to suburban Henderson.
Update 7.45am: At least two people have died and 24 more are injured with suspected gunshot wounds, a Las Vegas hospital spokesman confirmed to Reuters.
The shooting took place at the Route 91 Harvest Festival as country music artist Jason Aldean was performing.
Local media is reporting that one police officer has been shot.
Machine gun fire can be heard in a video posted online during the concert.
Flights to and from McCarran Airport have also been halted.
UPDATE: Flights in and out of @LASairport have been temporarily halted in response to reported shooting incident on Las Vegas Strip.— McCarran Airport (@LASairport) October 2, 2017
Earlier: Las Vegas police are investigating reports of an active shooter near Mandalay Bay Casino.
Reports indicate that several people have been taken to hospital with gunshot injuries.
It is believed the shooting happened at a country music concert.
What sounded like automatic gunfire could be heard in video from the scene posted on social media.
Police are asking members of the public to avoid the south end of the Strip.
Las Vegas Boulevard has been closed off at Tropicana, southbound past Russell Road.
We're investigating reports of an active shooter near/around Mandalay Bay Casino. Asking everyone to please avoid the area. #LVMPDnews— LVMPD (@LVMPD) October 2, 2017
Please avoid heading to the south end of the Strip. Las Vegas Blvd is shut down at Tropicana, southbound past Russell Rd at this time.— LVMPD (@LVMPD) October 2, 2017
More to follow.