One man died and at least seven men were stabbed during a concert in Dublin last night.
Detectives have not yet been able to identify the victim, who is believed to have died from a suspected drugs overdose at the Swedish House Mafia concert in the Phoenix Park.
Elsewhere three of the injured men remain in a serious condition in hospital after the knife attack.
A 23-year-old suspect was arrested over a number, but not all, of the assaults.
More than 45,000 fans packed out the open air venue for the concert, which featured Snoop Dog, Tinie Tempah, Calvin Harris and headlined with the electronic dance music group, Swedish House Mafia.
A Garda spokesman said a man in his 20s became ill and looked for medical attention from staff at about 7pm.
He was rushed to Connolly Hospital Blanchardstown where he was later pronounced dead.
“Gardaí have not been able to identify this man and are asking family and friends to check that loved ones have arrived home safely from the event,” he added.
Meanwhile gardaí said a minimum of seven men, all aged in their late teens or 20s, were stabbed between 8.30pm and 1am.
“A number of the victims required treatment at Connolly Hospital Blanchardstown and three people continue to be treated at the hospital,” he continued.
It is understood one of the men in his mid-20s was stabbed several times in the back.
A Garda spokesman said a 23-year-old man was arrested and is being detained at Blanchardstown garda station under Section 4 of the Criminal Justice Act 1984.
Several other people were also arrested during the evening for minor public order and drugs offences.
The city centre park has hosted a series of concerts this week, including the Stone Roses on Thursday and Snow Patrol and Florence & The Machine tonight.
Fianna Fáil Justice Spokesperson Dara Calleary called on Justice Minister Alan Shatter to urgently address what he called the rising levels of violence and anti-social behaviour in Dublin.
"To have seven concert goers stabbed in the space of a few hours is absolutely appalling," Deputy Calleary commented.
“There has been a very worrying trend emerging in Dublin in recent weeks of violent crime being perpetrated on innocent people, in many instances unprovoked and random," he added.
"It is only a couple of weeks ago that journalist, Eugene Moloney, was brutally assaulted and killed in another random attack.
“I am calling on the Minster for Justice to immediately establish a special Dublin Task Force to address the growing nature and frequency of these violent attacks," Deputy Calleary said.
"Dublin is fast getting a reputation for being unsafe at night and the Minister needs to act swiftly and come up with some measures to address the concerns of a lot of people in the capital."
Denis Desmond, managing director MCD Productions which promoted the gig, said every possible precaution was taken to ensure the safety and security of the crowd.
All CCTV footage captured in the area has been handed over to gardai and staff are fully co-operating with investigators.
“Obviously we are very disappointed that an individual or very small number of individuals engaged in anti-social behaviour, attempting to spoil the enjoyment of others,” said Mr Desmond.
“Such behaviour is certainly not reflective of the vast majority of the 45,000 fans who were extremely well behaved and should be congratulated.
“Unfortunately, anti-social behaviour has become more and more part of daily society with no town or village across the country escaping such conduct.”
Mr Desmond said MCD would work closely with gardaí and fully support their tactical operations in combating anti-social behaviour.
“Public safety is always our number one priority and we actively engage in detailed planning in advance to ensure this,” he continued.
“Ticket holders entering the site were subject to a search permissible by law. Every precaution as far as possible was taken to ensure the safety and security of the audience at all times.
“Despite our best efforts – with security and gardai personnel levels well in excess of the required numbers for a licensed event of this size – there is only so much one can do to combat anti-social behaviour
“We would like to wish those affected a full and speedy recovery,” he added.