PSNI chief inspector Mark McEwan has said a small quantity of suspected drugs was seized outside the Odyssey Arena in the wake of a major incident that saw 17 teenagers taken to hospital.
PSNI officers made three unrelated arrests last night.
A man aged 21 was detained for disorderly behaviour, another aged 18 was arrested for assault and resisting police arrest, and a 16-year-old woman was arrested for assault and resisting arrest. They are in custody at a city centre police station.
The episode unfolded when scores of heavily intoxicated children turned up to attend a rave event in the Odyssey Arena on the edge of the city centre last night.
Many were denied access to the venue, where Dutch electronic dance DJ Hardwell was playing, and the situation outside the building swiftly deteriorated, with medics, ambulance crews and charity volunteers providing first aid to more than 40 unwell young people.
A major incident was declared by the Northern Ireland Ambulance Service and in the city’s hospitals, where extra staff were called in to help.
Three of the teenagers admitted to hospital were subsequently discharged with the remainder expected to leave later today.
Police met arena managers, the private security firm in charge of the event and representatives from Belfast City Council and the SOS volunteer charity bus prior the concert, for which 10,000 tickets were sold.
A police drugs dog moved through partygoers in the queue to detect anyone trying to smuggle drugs into the venue.
Facilities were in place inside and outside to manage the welfare of vulnerable persons.
“Over the course of the evening, approximately 300 young people, some of whom had travelled to the venue by coach or other group transport, were showing signs of intoxication or were not the correct age and were not permitted entry to the venue,” Mr McEwan said.
“Any individuals that required medical assistance was provided with via the SOS bus and the Northern Ireland Ambulance Service staff.
“Sixty-eight people within the venue were also provided with medical assistance.”
Fifteen people were taken to the Royal Victoria Hospital in Belfast for treatment. Another three were taken to the Mater Hospital for treatment.
Police are meeting Odyssey Arena managers to review the incident and will be conducting an investigation. CCTV camera footage will form part of that process.
Mr McEwan added: “Police would encourage parents that may be considering allowing their child to attend an event where there is an age restriction to ensure that the child is the appropriate age.”
Colin Neill, chief executive of Pubs of Ulster which represents local bar owners, said: “Somewhere someone gave these kids alcohol I think it’s time to call an end to it.
“I think we need more than a police investigation, I think the Assembly need to get involved.”
Odyssey general manager Adrian Doyle said, as with any concert, the safety of patrons was an absolute priority at all times and the event control team was confident that it had sufficient staff on site to maintain a safe and enjoyable concert.
He said anyone who turned up to the event visibly drunk was not allowed in.
A spokesman for the Northern Ireland Ambulance Service said: “We believe the majority arrived suffering from too much alcohol.”
He added a number of people were unconscious at the scene.
Dr Tony Stevens, medical director at the Belfast Health Trust, paid tribute to staff in the Royal Victoria and Mater hospitals that were involved in the response.
“We handled it very well,” he said.
“I am very grateful to the large numbers of specialist staff that came in, and indeed all the staff – we had everybody from telephone operators to portering staff who were helping.”
Dr Stevens told Radio Ulster: “The busiest team were the ones answering the telephones because parents were unable to contact their children at the scene.”
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.
Last month dozens of fans camped overnight or queued for hours on a Belfast street in pouring rain for a ticket to his show.