Six fire crews went to the Alexander Maconochie Centre about 7.30pm on Wednesday to attend a fire at the jail but were stood down 90 minutes later.

"The incident started with a number of detainees behaving aggressively and not complying with officer directions," the Justice and Community Safety directorate said in a statement issued some hours later.

"Corrections officers acted quickly and professionally to resolve the incident."

Nobody was injured in the incident and resolution was achieved through negotiation, the directorate added.

"The matter was resolved when detainees became compliant with directions," the statement said.

Representatives from the Community and Public Sector union were outside the prison on Wednesday for many hours, gaining a first-hand insight into members' concerns as they came off shift after a long and troubled night.

"We were alerted to the issue around 8.30pm but the trouble started brewing mid-afternoon and gradually built up from there," the union's regional secretary Madeline Northam said.

"It started with the detainees becoming rowdy and having a go, and escalated.

"A fire was started in one of the [cell] blocks and the smoke then forced the detainees out into the yard."

Ms Northam said that the day shift remained on as the trouble flared but some of those staff didn't finish work until 1am, after starting their shift at 6am.

"What the staff need now is for the promises that were made back in November to be kept, the regular training programs started immediately, and appropriate kit provided to properly deal with these issues," she said.

It is the second major incident at the jail in six months. A riot broke out at the jail in November last year in which 27 prisoners armed themselves with broom handles and other implements.

Four fires were also lit and firefighters needed officers with riot shield protection as they fought the blazes.

In a subsequent report delivered in March this year, the ACT Inspector of Correctional Services Neil McAllister found there was a lack of support for staff, insufficient training and inadequate equipment. He made 13 recommendations.

The damages bill from the November riot was costed at $5.7 million.

It was later revealed the former head of Corrections at Canberra's jail had to apologise to his staff for failing to reveal to the public the seriousness of the November riot.

Former ACT Corrections commissioner Jon Peach has since been moved on from the most senior role at the prison, with 18 months of his contract left to run.

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