Two people have died after a St Patrick’s Day party at a hotel in Cookstown, Co Tyrone.
The Police Service of Northern Ireland said two other people were in hospital after the incident at the Greenvale Hotel, one in a critical condition and the other stable.
Many young people were believed to have been in attendance at the party.
While the circumstances of what happened are still under investigation, there were reports of a crush at the scene, police said.
Assistant Chief Constable Mark Hamilton said: “I can confirm there are two fatalities at this stage and a small number of other casualties.”
He added: “While the exact cause of the incident is still unknown, there are reports of a crush at the scene.”
Police posted on Twitter shortly after the incident, urging parents to pick up their children from the venue on Drum Road.
Emma Heatherington, whose two sons, aged 17 and 18, had been at the event, said she “felt sick” when she saw the police appeal.
“My two boys were there so I rang them, shaking, and thankfully got them both,” she said. “They were on their way home at that stage.
“They say there was a huge crowd waiting to get into the venue and then a lot of commotion up near the front of the queue, then they said the emergency services arrived and they were all asked to leave.
“They came home very, very shaken with rumours that some people had died.”
The 42-year-old, of Donaghmore, Co Tyrone, added: “While it’s not clear exactly what happened, it’s the most tragic ending imaginable to what was supposed to be a celebration of St Patrick’s Day.”
A member of staff at the nearby Glenavon Hotel said he had heard the sirens as emergency services rushed to the scene, and said police had come to borrow their defibrillator.
“There were ambulances passing our entrance,” he said. “It’s scary, and you just hoped everyone was OK.
“It’s very sad to hear what happened.”
Brendan Marshall, a local photographer, said the Greenvale Hotel was well known for teenage discos.
“(They have them) on special occasions such as St Patrick’s Day or around Christmas time,” he added.
The Northern Ireland Ambulance Service (NIAS) said it had received several calls from about 9.30pm on Sunday and sent two rapid-response paramedics, two doctors and five emergency crews to the scene.
Colin Neill, chief executive of Hospitality Ulster, said: “We are devastated to hear of the confirmed PSNI report of at least two deaths this evening at the Greenvale Hotel in Cookstown. This is shocking and tragic news and our thoughts and prayers are with the families of the deceased.”
Democratic Unionist Party leader Arlene Foster tweeted that her “thoughts and prayers” were “with everyone impacted by this tonight”.
And Sinn Fein deputy leader Michelle O’Neill called it a “parents’ worst nightmare”.
“My thoughts and prayers are with the families,” she added.
Former Democratic Unionist MP for South Antrim, William McCrea, said: “We’ve got to see what lessons can be learned from this tragedy.
“I drove past this 10 minutes before it happened, not knowing that 10 minutes later an absolute tragedy would happen.
“The people that I’ve spoken to, they’re very shocked. It’s a close-knit community.”