The ambulance service has declared a 'major incident' at Belfast's Odyssey Arena with up to 60 casualties suffering from the ill-effects of alcohol and drugs.
It's understood crews are dealing with a large number of casualties at the Belfast venue.
The Belfast Trust has now confirmed 14 young people are now at the Royal and Mater hospitals in a stable condition.
It's believed several people were taken to hospital for treatment.
Extra staff are also being brought in to nearby Belfast hospitals, including the Ulster and Royal Victoria, to deal with the high numbers of casualties.
DJ and producer Hardwell was performing at the arena this evening, with the show still continuing.
The Odyssey's general manager, Adrian Doyle said casualties were treated after arriving intoxicated to the concert.
He said they were not allowed entry.
"It is our understanding that a number of patrons arriving at the Odyssey Arena to attend a concert by Dutch DJ act ‘Hardwell’ have required medical attention, having arrived intoxicated at the Odyssey Complex," he said.
"These patrons were not granted entry to the Odyssey Arena, and were treated by the Ambulance Service outside. Seven patients have now been transferred to hospital by ambulance."
He said the Hardwell concert was still going ahead as normal.
Northern Ireland Ambulance Service spokesman John McPoland said: "We believe the majority arrived suffering from too much alcohol.
"We declared a major incident because of the number of resources we had to deploy to the scene."
According to former Belfast Lord Mayor, Niall O Donnghaile, several casualties were taken to hospital for treatment.
After speaking to the PSNI, he said on Twitter that bars within the arena had been closed.
Last month dozens of fans camped overnight or queued for hours on a Belfast street yesterday in pouring rain for a ticket to the Hardwell show at the Odyssey Arena.
Hardwell, aka Robbert van de Corput (25), was named the world's number one DJ in the 2013 DJ Mag Top 100 DJs Poll.
His hits include Spaceman, Three Triangles (Losing My Religion) and Apollo.
Anyone concerned regarding the incident can contact an emergency helpline on 028 90638131.
Colin Neill, chief executive of Pubs of Ulster which represents local bar owners, said he was concerned.
"Pubs of Ulster would reiterate that alcohol should be consumed responsibly and safely. Pre-loading at home before going out is dangerous and can lead to unintended consequences with people putting themselves at great risk," he said.
"Parents must stop under-18s getting access to drink and licensees should check ID and exercise extreme caution at all times.
"We urge pubs in Belfast to be extra vigilant this evening - be on the lookout for persons underage and do not admit young people possibly coming from the Odyssey who have had too much to drink."
DUP MLA Robin Newton called for a full report into the incident.
"The early reports of youngsters being ill spread like wild fire across the social media," he said.
"These reports will have caused concerns to parents whose sons and daughters were intent on attending this event.
"With up to 10,000 youngsters arriving at this event and with many arriving in bus loads from across Northern Ireland there is a need for effective communication on the wellbeing of our young people.
"I am grateful that the emergency services have put their plans into action and that young people are being treated at the scene or in local hospitals."
Alliance MLA Judith Cochrane said: "I am deeply concerned for the wellbeing of these young people. My thoughts are with them at this time. I hope they will all be able to make full recoveries.
"I would like to pay tribute to the work of the ambulance and hospital staff who have responded to this incident."