The Northern Ireland Ambulance Service has declared a major incident after up to 60 young people attending a concert in Belfast became ill.
A doctor and several ambulances are at the scene of the Odyssey Arena.
A number of people have been taken to hospitals across Belfast to be treated for the effects of drugs and alcohol.
They had been attending a dance event headlined by Dutch DJ Hardwell.
Last month dozens of fans camped overnight or queued for hours on a Belfast street in pouring rain for a ticket to his show at the Odyssey Arena.
Hardwell was named the world’s number one DJ in the 2013 DJ Mag Top 100 DJs Poll.
His hits include Spaceman, Three Triangles (Losing My Religion) and Apollo.