Three teenagers have died after reports of a crush at a St Patrick’s Day party at a hotel in Cookstown, County Tyrone.
A 17-year-old girl and two boys aged 16 and 17 died after the incident outside the Greenvale Hotel on Sunday night.
A number of other teenagers have also been treated in hospital.
The police said a large group of young people had been waiting to get into a disco at about 21:30 GMT. One of the teenagers died at the scene.
“Our preliminary investigations show there was a crush towards the front door of this hotel, and in that crush people seem to have fallen,” said Police Service of Northern Ireland Assistant Chief Constable Mark Hamilton.
“There seemed to be a little bit of struggling going on to get people up off the ground and that might explain also why there was a report of some fighting.”
He added: “It is heartbreaking that an event which should have been fun for these youngsters on St Patrick’s night should end in such a terrible tragedy.”
A teenage eye witness, who did not wish to be named, told the Ulster Herald he was waiting outside the hotel when a “stampede” started.
“We were all outside waiting for the gate to open and get in,” he told the paper. “Then everyone just started swaying back and forth and pushing from side to side.
“Suddenly there was a rush forward and the whole queue collapsed and everyone fell to the ground.”
The teenager said he was pinned to the floor with other people on top of him and unable to move for 20 minutes, adding that there were more than 100 people involved in the queue crush.
Northern Ireland Ambulance Service’s Medical Director Dr Nigel Ruddell said: “Everything points towards it being a tragic accident.”
“It was clearly a very distressing scene for all those who were caught up in the midst of it,” he added.
He thanked ambulance crews who worked through the night despite having dealt with “a very difficult situation”.
The focus of the police investigation is on eyewitness accounts of what happened and CCTV footage from outside the hotel.
Although the CCTV images are dark, they do provide an indication of what went wrong.
Detectives are studying the footage frame by frame.
It appears the people who died sustained injuries in a crush as a large crowd waited outside the disco, hoping to get inside.
However, although there are images of people falling, police need to be sure that they are the teenagers who later died.
There are also reports of fighting briefly breaking out.
It is a complex investigation and detectives want more people who witnessed what happened to come forward.
The hotel was hosting a party for young people to celebrate St Patrick’s Day.
Paramedics, doctors and five emergency crews were dispatched to the venue at about 21:30.
In a Facebook post at 22:41 GMT, the police asked parents to collect their children from the hotel immediately.
ACC Hamilton said the Northern Ireland Ambulance Service had received a 999 call on Sunday night with reports of people injured outside the hotel.
They declared it a major incident and police, the fire service and environmental health staff then also attended the scene.
