Offenders trash Vic youth prison offices

Detainees were locked down at the Malmsbury Youth Justice Centre on Thursday night after someone was found making a shiv.

But the Community and Public Sector Union says when the lockdown was lifted, four of the offenders started trashing staff offices.

A special response team from the Parkville youth prison was sent to Malmsbury at 9pm to calm the riot.

The union says the four offenders have since been sent to Barwon Prison's Grevillea Unit.

Victoria Police said it had a report of two people allegedly causing damage and making threats.

"Investigators have spoken to both youths, aged 18 and 19, and both are expected to be charged with criminal damage and unlawful assault," a police spokeswoman said on Friday.

Youth Affairs Minister Jenny Mikakos' office directed questions to the Department of Health and Human Services.

"There were no injuries to staff or clients and at no point was there a risk to security of the facility," a DHHS spokeswoman told AAP.

Opposition children's spokeswoman Georgie Crozier said Ms Mikakos must be sacked over her handling of youth justice.

"There is now no doubt that (Premier) Daniel Andrews and his incompetent minister have been covering up a disaster of his government's own making," Ms Crozier said.

The latest destruction comes after a series of riots at Parkville and Malmsbury forced the government to decide to move about 40 offenders to Barwon Prison, a maximum security jail near Geelong.

The teens are being housed in the Grevillea Unit, which is a standalone building within the prison, with separate entrances, exits and exercise yards, away from the main adult population.

Repairs to Parkville and Malmsbury, and planned fortification works, are set to cost Victoria $10 million.

The government is also going to build a new youth prison to replace the Parkville facility, either on the Parkville site or somewhere else.

Originally published as Offenders trash Vic youth prison offices