The PSNI said over 300 people arrived at the DJ Hardwell concert in the Odyssey Arena on Thursday night either drunk, on drugs, or were underage and were barred from entry into the venue.
Over 100 people required medical treatment and given the large volumes of those requiring aid the emergency services had to declare a major incident and erect a special temporary medical facility in the grounds of the Queen's Island complex.
The DJ went on to play in Dublin on Friday, however, it has since emerged that the concert in Edinburgh on Saturday night has been cancelled because of the incident in Belfast.
The Scottish promoters, Colours, said they were working to try and re-schedule the event after the authorities decided to withdraw their licence.
In a statement, the promoter said: "Due to the situation in Belfast on Thursday, 6 February, it was decided that the event in Edinburgh should not go ahead due to safety concerns."
Meanwhile, the DJ's concert in Dublin on Friday is to go ahead as scheduled, however, extra police have been drafted in as a precautionary measure.
Following the Belfast incident, the promoters for the Odyssey concert issued a statement on the DJ's Facebook page.
"We would like to emphasize the fact that the visitors of the concert and Hardwell himself were not aware of this situation that mostly took place outside the venue and which was the result of a strict door policy," they said.
"Visitors inside the venue have been safe at all times and the visitors whom we have denied access received all the medical attention and care they were in need of.
"We always try to implement a zero tolerance policy when it comes to substance abuse and the events yesterday are a direct result of that policy."
Nine people remained in hospital on Friday where their conditions have been described as "stable".
The ambulance service dealt with casualties "at varying levels of consciousness" at the dance event.
Paramedics treated 40 people outside the Odyssey, while another 68 individuals received aid from the private medical team inside the concert.
John McPoland, from the NIAS, said they were alerted by staff at the SOS bus after a number of people arrived intoxicated shortly after 8pm.
"What made this unique was the sheer number of people at the one scene," he said.
"Normally, we would deal with people suffering from alcohol and perhaps drug abuse on a regular basis on weekends right across Northern Ireland, but never in the one place.
"It seems that a lot of the young people turned up already with lots of alcohol on board."
There were girls being carried out that were just completely out of it, there were boys inside the Odyssey itself fighting with people ...
Pauline O'Boyle, parent
Doctors were put on standby at the Ulster, Mater and Royal hospitals and extra staff were called in.
Dr Russell McLaughlin, consultant at the Royal Victoria Hospital's A&E, told UTV the patients' symptoms were "consistent with drug and alcohol misuse".
The Odyssey said that 9,500 tickets were sold for the event and a number of concert-goers arrived at the venue already intoxicated and were not admitted.
A temporary treatment facility was established in the grounds of the complex for those needing attention.
It's believed to be the first time a medical facility of that kind had been put in place for such an emergency.
Odyssey Arena general manager Adrian Doyle, said: "As with any concert, the safety of our patrons is our absolute priority at all times and we are very confident that we have sufficient staff on site to maintain a safe and enjoyable concert."
He said the concert continued "as normal inside the Odyssey Arena".
Eye-witness footage captured fights that broke out among the young revellers inside.
Mr Doyle said thorough pre-planning had taken place with the relevant authorities, including the police.
Stringent ID checks were in place under the 'Think 21' guidelines for any patrons wishing to purchase alcohol within the Odyssey Arena, with patrons required to produce a valid passport or driving licence as proof of ID.
Odyssey Arena manager Adrian Doyle
He added: "Decisions were taken at this meeting, to ensure safety, caution and good management of the event and a detailed management plan was agreed and put in place.
"Both the PSNI and Community Enforcement Teams from Belfast City Council were on the ground at the event confiscating alcohol that was in the possession of patrons as they arrived at the Odyssey.
"In anticipation of any patrons being turned away at the door for any reason, the support services of the SOS bus were also deployed.
"High levels of staff were employed to manage queues at the door.
"Searches were carried out on the door by a team of Security Industry Authority accredited personnel, with two PSNI sniffer dog teams also deployed.
"Large numbers of patrol and response staff were on the concourses and in the main hall throughout the evening and supervisors checked toilet facilities on an ongoing basis."
He continued: "Purchase of alcohol was limited to two drinks per ID, and all alcohol sales were stopped at 9pm.
"Incident levels inside the Odyssey Arena before, during and after the Hardwell concert were at normal levels for an event of this size and nature and were managed effectively at all times by staff."
Fifteen of those treated were taken to the Royal Victoria Hospital. Another three people were also taken to the Mater Hospital for treatment.
On Friday, a spokeswoman for the Belfast Trust said nine people, including two 16-year-olds, remained in the Royal and Mater hospitals. She described their condition as stable.
The police will be meeting with the Odyssey Arena's management to review the incident and are investigating.
On the night, three people were arrested and a small quantity of suspected drugs was seized in the area outside the venue.
A 21-year-old man was arrested for disorderly behaviour, an 18-year-old man was arrested for assault and resisting police arrest, and a 16-year-old girl was arrested for assault and resisting arrest.
All three individuals are currently in custody at Musgrave Police Station.
Pre-loading at home before going out is dangerous and can lead to unintended consequences with people putting themselves at great risk.
Pubs of Ulster
Pubs of Ulster condemned what happened and warned young people of the dangers of "pre-loading" - drinking large amounts of alcohol before heading out.
Chief Executive Colin Neill said: "We are extremely concerned to hear that a large number of young people were treated for the apparent effects of alcohol and drugs.
"Pubs of Ulster would reiterate that alcohol should be consumed responsibly and safely.
"Parents must stop under 18s getting access to drink and licensees should check ID and exercise extreme caution at all times."
The organisation also called for those found responsible for allowing those underage to drink alcohol to be prosecuted.
It is understood doors to the over 16s event opened at 6.30pm.
Emergency services remained on stand-by after the concert ended.
Pauline O'Boyle, from Waterfoot in Co Antrim, took her two sons aged 16 and 17 to the concert, but returned after hearing reports of the major incident.
"As we arrived, we were quite concerned about the ones that we had seen - you kinda knew to look at them, they were on something. Either drink or drugs or something," she said.
"I didn't expect this. It's quite scary as a parent."
Police are meeting with Odyssey Arena to review the incident and will be conducting an investigation. CCTV will form part of that process.
At the scene, Belfast councillor and doctor John Kyle added: "This is clearly a major concern - we need to find out what exactly happened.
"But if this was precipitated by drug use, then that is very concerning and we need to look at where the drugs have come from, what they were, and who was selling them."
The PSNI said that prior to the concert - as is usual procedure in events of this size - officers met with officials from the Odyssey Arena, security organisation Eventsec, Belfast City Council representatives, and those involved with the SOS bus.
Officers were deployed in the area outside the venue and a police drugs dog moved through the queue to detect anyone who may have had illegal substances on them.
Area Commander Chief Inspector Mark McEwan said: "There were facilities in place both 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.
"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."
On his official Twitter account, DJ Hardwell made no direct reference to the incident at the Belfast gig.