Seven staff at the Bimberi Youth Justice Centre were taken to hospital after an incident that's been described as a "riot".
The incident involved staff and young people at the detention centre, although authorities have not said what the incident was or how many detainees were involved.
Four staff were taken to Canberra Hospital in a stable condition, while a further three were sent to Calvary Hospital with minor injuries.
It took police two hours to secure the detention centre following the incident.
The incident triggered an ambulance bypass at Canberra Hospital from 8.30pm, with the hospital already experiencing high demand at the time of the incident.
The bypass lasted for about two hours and a code brown was issued. A code brown, according to ACT Health, is an emergency management plan activated for external disasters.
All seven Bimberi staff were discharged from hospital before midnight.
It's understood more than 100 people were waiting in the emergency department at Canberra Hospital before the ambulance bypass was put in place, with the department operating at capacity.
New arrivals to the hospital were told see their GP the next day if their case wasn't serious or urged to go to a walk-in centre instead.
Separate investigations into the incident at Bimberi have been launched by ACT police and WorkSafe ACT.
Police are investigating whether charges would be laid as a result of the incident.
Crisis meetings were being held on Tuesday between directorate and WorkSafe staff over the incident.
Youth and Health Minister Rachel Stephen-Smith did not say what the cause of the incident was but said it was "significant".
She said it was described as a riot in some of the operational advice sent between agencies on Monday night.
"I think it's too early to make a comment about the appropriateness of that description at this stage," Ms Stephen-Smith said.
She was not able to provide specific information about the "major incident" including how many detainees and staff were involved.
Ms Stephen-Smith said she commissioned an investigation into the incident by Peter Muir, a former director general of the Department of Juvenile Justice in NSW.
"I can confirm that the incident did involve a number of young people at the centre as well as a number of staff," she sad.
"It was classified as a major incident which does mean that all staff were involved and that external support from ACT policing was required in order to secure the centre."
ACT work safety commissioner Greg Jones said four WorkSafe officers attended Bimberi overnight following the incident.
"Officers aren't there this morning, we're letting police and correctional officers deal with the situation, and obviously police are obtaining whatever evidence they need," Mr Jones said.
"We'll start our investigation with paper work and procedures once the police have finished theirs."
Mr Jones said the incident started after a number of detainees came out of their cells, before a "mass altercation" with Bimberi staff.
"Workplace injuries is a significant concern for us, and we'll be finding out what circumstances led to those injuries," Mr Jones said.
Canberra Liberals youth and community services spokeswoman, Elizabeth Kikkert, said she was shocked upon finding out about the incident, but not surprised that it happened.
Ms Kikkert said staff had told her a series of similar smaller incidents had taken place at Bimberi over recent years and months.
"Staff have been sharing stories that they are not receiving adequate training to deal with an incident like when they're dealing with aggressive young people, as well as the lack of staff as well," Ms Kikkert said.
"More staff need to come in and alleviate the staff that are already working over time."
Ms Kikkert said a pattern was emerging at Bimberi of stressed and burnt out staff and instances of youth detainees attacking staff.
Briefings were held for the ACT Opposition with directorate over the incident on Monday afternoon.
With separate reviews being undertaken into the suspected riot, Ms Kikkert said a combined approach was needed to come up with recommendations and to prevent future incidents from happening.
The ACT regional secretary for the Community and Public Sector Union, Madeline Northam, said Bimberi staff were in shock following the incident.
Ms Northam said staff had been calling out for more training to be able to deal with situations similar to the one seen on Monday night.
"Our members have raised concerns about how regular the training is," Ms Northam said.
"The example we're hearing most is they want use-of-force training, which is training how to restrain young people when an incident is occuring, and the feedback we're getting is staff are crying out for more."
Ms Stephen-Smith said the incident was not triggered by or related to a previous incident where a 17-year-old detainee receiving treatment at Canberra Hospital escaped custody in the early hours of Monday morning.
The teenager escaped custody from the hospital about 2am and was found three hours later on Parkes Way.
"It's probably not linked, but we're getting further information," Ms Stephen-Smith said.
Deputy opposition leader Nicole Lawder said she was concerned for the health and wellbeing of staff after the "riot".
"Also the residents at Bimberi, it could be completely traumatising for them as well," she said.
"The government has serious questions to answer."
Ms Lawder said said the pressure the incident placed on Canberra Hospital showed a lack of planning from the government.
"Our health and hospital system seems to be lurching from one crisis to another," she said.
"Ambulance bypass is a contentious issue, in Victoria for example they've stopped it because they're concerned about the health outcomes of people who have been moved forward to a different hospital.
"It's a lack of adequate planning and forethought from the minister."
The Community Services Directorate says it will work with authorities while investigations are under way.
Counselling will be offered to Bimberi staff affected by Monday night's incident.
"The safety and care of young people and staff at Bimberi remains the number one priority," a spokeswoman said.
"Assistance and support continue to be provided to young people and staff."