Georgia has become the latest U.S state to be placed on hurricane alert.
The governor Nathan Deal has already ordered a mandatory evacuation of the city of Savannah and other coastal areas as Irma approaches.
Queues for petrol have been forming across Florida as people prepare to leave before Hurricane Irma hits at the weekend.
State governor Rick Scott has warned people not to defy mandatory evacuations - saying "we can't save you once the storm hits."
He has told people in those areas "if you're still at home, LEAVE!"
Hurricane Irma is surging through the Caribbean, leaving a path of destruction in its wake. pic.twitter.com/07UWtYoTJ0— HuffPost (@HuffPost) September 7, 2017
One million people across the Caribbean are said to be without power after the hurricane swept through islands, leaving 10 people dead.
The killer storm has already caused devastating damage to Barbuda, St Martin and the British Virgin Islands and now it is due to make landfull on the islands of Turks and Caicos home to more than 30,000 people.
Hurricane Irma has killed at least 10 people on a number of Caribbean islands, which have suffered extensive damage from the category five storm.
Airports, hospitals, and schools have been badly affected on the British Virgin Islands and Anguilla.
60 percent of residents on Barbuda are homeless, and France's Interior Minister Gerard Collomb says they'll need to rebuild both St Martin and St Barts.
The Government has bolstered the funds available to deal with the aftermath of Hurricane Irma to £32 million, the British Prime Minister has said.
Theresa May announced the cash injection to the relief effort following a meeting of the Government's emergency Cobra committee on Thursday afternoon.
The deadly storm continues to lay waste to swathes of the Caribbean, including British overseas territories.
Mrs May said her "thoughts and prayers" were with all those affected.
Hundreds of British military personnel have been deployed to the Caribbean to help clear roads and restore power after Hurricane Irma.
There are no reports of any injuries or deaths of Irish citizens in the affected areas but the Department of Foreign Affairs says if you have concerns about Irish people in the region you can contact the Department in Dublin on 01 408 2000.
At least 10 people have died as Hurricane Irma continues to tear a deadly path through the Caribbean, with Florida on high alert.
The storm destroyed nearly all buildings on the island of Barbuda on Wednesday, killing a two-year-old child as a family tried to escape, before wreaking havoc on the French territories of St Martin and St Barts.
At least eight people were killed and 23 injured in French Caribbean island territories, while one death was reported in the nearby island of Anguilla, a British overseas territory that was among the first islands to be hit.
Emergency attempts to reach Caribbean island communities devastated by Hurricane Irma could be affected by a second major storm threatening the region.
According to the United Nations up to 37 million people could be affected by the historic hurricane that has left at least seven dead and thousands homeless.
Irma, a category five hurricane, is expected to have passed over the Caribbean by Friday, however Hurricane Jose is expected to follow a similar path when it arrives over the weekend.
The category one storm is currently building in intensity in the north Atlantic, around 900 miles east of the Lesser Antilles where the island of Barbuda saw catastrophic damage on Wednesday.
It is feared the storm may strengthen to a potentially devastating category three hurricane, which can bring winds of up to 129mph.
UK Met Office meteorologist Greg Dewhurst said: "Jose is currently forecast to follow a similar track initially to Irma, moving westwards in the Atlantic and to the north and east of the Caribbean where the hurricane was on Wednesday.
Hurricane Irma is continuing its devastating path over the Caribbean.— BBC Radio 5 Live (@bbc5live) September 7, 2017
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"Jose's a couple of days away and the track may change, but it's forecast to come close to those islands over the weekend."
While Irma has followed a path expected to take it toward the US state of Florida, Jose is expected to swing back out into the Atlantic after grazing Puerto Rico on Saturday night.
Mr Dewhurst said: "Jose is currently a category one hurricane and it is expected to be a category three by Friday and drop back down to a category two by Saturday.
"It may not make landfall and its outer edge may only reach land. Either way there may be a risk of strong winds and rain for the north east of the Caribbean.
"Obviously Jose coming in could hamper the clearing-up process. It's one they will be keeping a very close eye on."
While the Caribbean faces the possibility of being affected by a second major hurricane, Mexico is braced for the arrival of Hurricane Katia.
The category one hurricane was headed for coast of Veracruz state where it expected to make landfall on Friday evening.
Hurricane Irma is continuing to tear a deadly path through the Caribbean as the scale of devastation in its wake begins to emerge.
The historic storm destroyed nearly all buildings on the island of Barbuda on Wednesday, killing a two-year-old child as a family tried to escape, before wreaking havoc on the French territories of St Martin and St Barts, leaving at least seven dead.
Tourists in the region have been urged to follow evacuation orders, while states of emergency have been declared in Puerto Rico, Cuba and Florida - amid fears Miami could be struck directly by the hurricane.
Meanwhile Sir Richard Branson was counting the cost of widespread damage at his private retreat in the British Virgin Islands after the category five hurricane pounded the archipelago.
A massive operation is underway to evacuate people away from coastal areas on Haiti and the Dominican Republic, where aid workers are moving residents into temporary shelters before the storm hits.
On Thursday morning Irma's eye was just north of the coast of Puerto Rico, lashing the island with heavy rain and high winds and leaving more than 900,000 people without power.
There were fears that the eye could come within 35 miles of the capital San Juan, bringing gusts of up to 100mph.
Irma is moving at around 16mph on a course forecast to take it toward the Bahamas and the British overseas territory of the Turks and Caicos Islands.
An alert sent by the Department of Disaster Management and Emergencies on Grand Turk urged residents near the coasts to take shelter on higher ground, warning the storm surge could raise water levels by 15 to 20 feet above the normal tide.
Some US government personnel have been ordered to leave the Bahamas before the hurricane's arrival, expected on Thursday night local time.
On the US mainland authorities fear the hurricane may slam into the Florida peninsula over the weekend, just days after storm Harvey devastated Texas.
Officials are making preparations to potentially shut down two nuclear power stations in the Sunshine State, while evacuation orders have been given in the Florida Keys.
Donald Trump, whose Mar-a-Lago resort in Palm Beach could be affected by the storm, said his administration is monitoring Irma closely.
"It looks like it could be something that could be not good, believe me not good," the US president said.
With sustained winds of 185mph, the category five hurricane is the most powerful Atlantic Ocean hurricane on record.
It is only the second time anywhere in the world a storm has been recorded maintaining such windspeeds for more than 24 hours, after typhoon Haiyan in 2013, according to an expert at the University of Colorado.
Antigua and Barbuda Prime Minister Gaston Browne told the Associated Press that nearly every building on Barbuda was damaged when the hurricane passed overhead, leaving around 60% of the island's approximately 1,400 people homeless.
Barbuda had been left "barely habitable", he said.
French President Emmanuel Macron said he expects that victims and heavy damage will be discovered on islands of Saint Martin and Saint Barthelemy, known as St Barts.
Briton Alex Woolfall hid in a concrete stairwell as the hurricane hit while he was on holiday in St Maarten, the Dutch area of the island.
He tweeted: "My god this noise! It's like standing behind a jet engine! Constant booms & bangs. At least concrete stairwell not moving."
Anguilla's tourist board said its major resorts had survived the storm, although many private homes had been damaged. There were no reports of any deaths.
A British naval ship has been deployed to help deal with the aftermath with 40 Royal Marines on board, as well as army engineers and equipment, as authorities struggle to bring aid to smaller islands.
British Foreign Secretary Boris Mr Johnson said in a statement: "I've just spoken to the Chief Minister of Anguilla to discuss the devastating impact of Hurricane Irma. My thoughts are with all those affected and the UK is taking swift action to respond.
"We have staff and a British naval ship ready to help those in need. Brits should follow our travel advice which will be regularly updated."
Before the hurricane's arrival Sir Richard refused to his Necker Island retreat and said he would be seeking shelter in the wine cellar with his staff.
His son, Sam, later wrote on Instagram: "Glad to say that all humans on Necker are ok although a lot of buildings destroyed. Very concerned for our friends and everyone on the neighbouring islands and people in its path. Please don't take this hurricane lightly if it is heading your way."
Christian Aid is helping to orchestrate the mass evacuation of Haiti and the Dominican Republic.
The charity's country manager, Prospery Raymond, said: "People are being moved to schools and churches for safety but in some areas, especially in the north west of Haiti, these buildings will not withstand the force of the storm."