Overtime hours for corrections officers at Canberra's Alexander Maconochie Centre have more than tripled in the past five years, costing almost $7 million in overtime pay.

Five years ago corrections officers did 8295 overtime hours, but this jumped to 30,138 hours in 2019-20.

Overtime hours are on track to be even higher this financial year, as so far guards have done more than 25,000 hours.

The public sector union said more staff needed to be urgently employed, as the shortage was forcing rolling lockdowns and making the jail an unsafe workplace, while the ACT opposition accused the government of mismanagement over the "staggering" increase.

Corrections Minister Mick Gentleman conceded the overtime hours were concerning and said immediate changes were needed to relieve the burden on officers.

Community and Public Sector Union regional secretary Maddy Northam said prison guards had been calling for more staff for years.

"What that means is existing staff are having to work longer and longer hours: that's not sustainable," she said.

As well, Ms Northam said the understaffing had resulted in more rolling lockdowns for detainees.

"It means detainees become more agitated, which means it's not a safe workplace for our members or for other detainees," she said. "We really, really need to make sure we get new officers on the ground as quickly as we possibly can."

Pressures on staff at Canberra's prison have been the subject of a series of recent damning reviews.

A report into a prison riot in November last year found fewer than 10 per cent of staff felt they were adequately trained to respond to the incident, which saw several fires break out at the prison and resulted in a $5.7 million repair bill. Another report found prison officers responsible for transporting prisoners lacked the appropriate training and policies were out of date.

ACT opposition corrections spokeswoman Elizabeth Kikkert said the government had failed to adequately staff the prison and left prison guards with no choice but to work overtime.

"The amount of overtime worked by our stalwart correctional officers at the Alexander Maconochie Centre is staggering. The rapid escalation of overtime hours worked even more so," she said.

"Our correctional officers have missed out on valuable training through no fault of their own because there is not enough staff at the Alexander Maconochie Centre to allow officers the time they deserve to receive important training.

"It is paramount that the AMC has adequate staff to allow for training and rest for our correctional officers to avoid chronic stress, which could lead to serious health issues."

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In response to problems at the prison, the ACT government has developed an oversight committee that will seek to address staff and training problems at the prison.

It will be led by Victoria's former top police officer Christine Nixon.

It will also comprise ACT Corrective Services staff, the union and oversight bodies.

Mr Gentleman said the committee had its first meeting last month, which he called "very productive".

"Members are working to develop a blueprint for change within the Alexander Maconochie Centre and Court Transport Unit and overseeing the implementation recommendations from recent reports and inquiries," Mr Gentleman said.

As well, Mr Gentleman recognised the pressure guards were under and said a recruitment effort was under way to employ more corrections officers.

"The increase in overtime for corrections officers is concerning and demonstrates the pressures they are under," he said.

"We are working to implement changes to relieve this pressure, including recruiting more corrections officers."

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