Emergency services, including police and firefighters, are currently at the correctional facility and have advised the public to steer clear of the area.
There are reports that at least one youth detention staff member was injured in the breakout.
The CFA said it was helping police with a job at the Malmsbury Youth Justice Centre on Wednesday afternoon.
The youth jail has been damaged in previous riots, which have also affected the Parkville youth detention centre.
Victoria will recruit 41 new youth justice workers after a leaked report found endemic staff shortages led to riots at the centres.
The report was ordered after riots at Parkville in March 2016, and Fairfax Media reports the government expected more riots due to low staff numbers and frequent "lockdowns" that incite unrest.
"We have boosted staff numbers and we're introducing new laws that will see tougher sentences for offenders who assault our dedicated staff," a government spokesman told AAP on Wednesday.