Two people have died following a St Patrick’s Day party at a hotel in Cookstown, County Tyrone.
A further four people were taken to hospital following the incident at the Greenvale Hotel.
The hotel was hosting a party for young people to celebrate St Patrick’s Day.
The Police Service of Northern Ireland said the exact circumstances were still under investigation, but the ambulance service said it was called after reports several people were unwell.
Paramedics, doctors and five emergency crews were dispatched to the scene at around 21:30 GMT.
In a Facebook post at 22:41 GMT, the PSNI asked parents to collect their children from the hotel immediately.
It had been widely suggested on social media that several young people had sustained crush injuries.
However, a journalist at the scene, Brendan Marshall, said the DJ who was performing at the event insisted to him that this was not the case.
“He confirmed that – contrary to the rumours that had been circulating – there had been no crushing and nothing had collapsed,” Mr Marshall told BBC News NI.
“He told me that a number of young people had become seriously ill. He said one young person was brought to him by a friend to have their pulse checked.
“The DJ then shone a light in their eyes to check whether they were alive.”
At the scene
by Mark Simpson, BBC News Northern Ireland
There is a huge sense of shock around the town.
Reports began circulating at 22:00 GMT that people had died. The news of two fatalities was confirmed by police just after midnight.
There were distressing scenes as some people who knew those who died broke down in tears at the police cordon.
A representative of the nearby Glenavon Hotel said the PSNI borrowed its defibrillator.
Democratic Unionist Party leader Arlene Foster tweeted that her “thoughts and prayers” were “with everyone impacted by this tonight”.
Speaking from outside the hotel, UUP councillor Trevor Wilson said: “I’m getting conflicting reports from people about what exactly happened, but there’s clearly a deep sense of shock here tonight that an event for young people just wanting to celebrate St Patrick’s night went so horribly wrong.”
Colin Neill, chief executive of Hospitality Ulster, said on Sunday night: “We are monitoring the situation closely and echo the PSNI appeal to parents to make contact with their children and collect them immediately from the venue.”