A stand-off over pool time as temperatures soared over the weekend has been blamed for another riot at a Melbourne youth justice centre.
Teenage criminals broke pool fencing and armed themselves with metal poles after refusing to get out of the pool on Saturday afternoon.
When the troubled youths then went back to their cells they used the poles to break through the ceiling and gain access to the roof cavity where they were able to break another detainee out of his cell.
Staff at the Parkville centre were evacuated and Victoria Police's public order response team and dog squad were called in to bring Saturday night's riot under control.
It was the third riot in a youth detention centre in the past few months, with previous disturbances leading the Victorian government to transfer some teenage offenders to the adult Barwon Prison.
Youth Affairs Minister Jenny Mikakos on Monday rejected opposition calls for her to stand down over the riots.
"The Liberals are once again more interested in lies and smears than the facts," she said in a statement to AAP.
Ms Mikakos said Parkville was built to be a residential facility and it wasn't meant to handle hardcore, recidivist offenders.
"It is ridiculous to have locked offenders, locked in their cells, being able to break through ceilings and get out," she told 3AW.
"That's what happened on Saturday and it's a recurring issue. We want to make sure this behaviour doesn't continue."
The teens had refused to get out of the pool when their time was up on a 37C day, so they were locked down in their cells until the evening, the union representing detention centre workers says.
When released from the lockdown, the teens were able to play basketball but returned to the pool unauthorised, a Community and Public Sector Union spokesman told AAP.
Police calmed the riot early on Sunday morning and seven prisoners were moved to the Grevillea Unit at Barwon Prison and the Malmsbury youth detention centre.
Ms Mikakos said there' had been contractors on site since November working round the clock.
"We have to fortify every single accommodation unit," she said.
Opposition children spokeswoman Georgie Crozier says Ms Mikakos should resign or must be sacked after the series of riots.
"Instead of getting tough on these repeat offenders that Jenny Mikakos calls 'the worst of the worst' the Andrews government is rewarding them with pizza, video games and pool parties," Ms Crozier said in a statement on Monday.
