The owner of the Greenvale Hotel - where three teenagers lost their lives - gave CPR to the victims.
Cheerleader Lauren Bullock, 17, keen sportsman Connor Currie, 16, and Morgan Barnard, 17, from Dungannon in Co Tyrone, died.
Police said it appeared that people had fallen and then been fatally injured, but are still investigating the cause.
Several hundred people were trying to get into the venue, Greenvale Hotel in Cookstown, Co Tyrone, after being dropped off by buses shortly before 9.30pm on Sunday.
A teenager who witnessed a crush said it was the most frightening moment of her life, after three people were confirmed to have died.
She said: "As I looked down I could see multiple bodies underneath me and as I looked up I could see multiple bodies on top of me.
"It was the most traumatic, frightening and stressful moment of my life."
Emergency services attended within minutes and attempted to resuscitate the victims.
Two were taken to hospital critically ill but died later. One died at the scene.
Northern Ireland Ambulance Service's medical director Dr Nigel Ruddell said: "Everything points towards it being a tragic accident."
People struggled to get off the ground and there was confusion, the Police Service of Northern Ireland (PSNI) said.
Assistant Chief Constable Mark Hamilton said: "It is a truly awful incident, heart-wrenching for everybody, particularly the families.
"Everybody did their best for them last night but it is a truly appalling incident.
"Unfortunately three are dead. The last person died this morning, unfortunately, with his parents near him."
Mr Hamilton said preliminary investigations showed there was a crush towards the front door of the hotel, and in that crush people seem to have fallen.
Security camera footage is being examined and police have appealed for videos captured by those present.
Lauren was a "beautiful soul" who was the backbone of her cheerleading team, a social media post said.
Her cheerleading team added: "My heart is broken writing this. You were the most down to earth, beautiful soul and our Coral team will never be the same without you."
She was a pupil at St Patrick's College in Dungannon. Principal Catherine McHugh described her as a "shining light".
"She was a leader among her peers and a quiet, strong and loyal presence. A treasured friend and capable young lady with a bright future."
Edendork Gaelic Athletic Association football club said it was devastated to hear of the death of "much loved and highly thought of" player and member Connor.
It said: "Connor will forever be remembered with the greatest affection by all associated with our club and indeed the wider Edendork community."
A relative of Morgan said he was a keen soccer player.
He added: "He was just a bundle of joy, always bouncing around, he seemed to have a lot of energy in him - a gentleman, he was.
"I am gutted. I just could not take it in, I tried to sleep and I could not sleep."
The hotel can take up to 500 people and attracts people from across the country.
Hotel owner Michael McElhatton gave CPR to the victims.
He has now given a short but emotional press conference at the hotel about the tragedy.
“We are all deeply shocked and saddened by the traumatic events of last night,” he told the media outside the business, his voice breaking.
“We offer our heartfelt sympathies to the families and friends of the three young people who have lost their lives.”
“The management and staff are assisting the police in their investigations.
“And I would like to place on record our appreciation for the speedy response of emergency services for last night’s terrible events.”
He declined to answer any questions from journalists before returning to the hotel. Police have maintained a presence at the hotel entrance since Sunday night.