Three teenagers have died following reports of a crush at a St Patrick's Day party in County Tyrone.
The victims are a girl and a boy of 17 and a 16 year old boy.
A teenage girl is also in hospital.
Officers are trying to work out what happened at the hotel in Cookstown last night.
They've asked anyone who was there not to share any video footage online.
ACC Mark Hamilton extends condolences to the families of the three teenagers who died at a St. Patrick’s Day event in Cookstown. A major investigation is now underway. pic.twitter.com/UiktCkx4IU
— Police Service NI (@PoliceServiceNI) March 18, 2019