A union spokesman said in an email that anecdotal reports indicated that since January an average of one worker per week was involved in a serious altercation with clients, often resulting in the worker seeking compensation from the department.

Overcrowded prisons, inconsistent management responses and a lack of consequences for those who committed violent acts all contributed to the problem, he said.

"The lack of consequence for the clients after they bash someone means they are bolder and more prone to resort to violence than before," he said.

"As a result, youth justice workers no longer feel supported by management because they are not taking appropriate action against clients who assault staff."

He said staff were not being given adequate training on how to prevent clients from becoming aggressive and that as the majority of workers were female they often didn't have the physical strength to restrain violent offenders.

Opposition spokeswoman Jenny Mikakos said the system was at breaking-point.

"[Community Services Minister] Ms Wooldridge says she has addressed the violence problems at Malmsbury but the fact is the system approaching breaking point, with more staff injured, off work and at-risk than ever before," she said.

"The issues at Malmsbury are because Ms Wooldridge is increasingly relying on inexperienced casual staff in what can be a dangerous and complicated environment.

"It is more evidence Ms Wooldridge isn't providing the staff the support and resources needed to do the job safely and effectively. 

"This is obviously a terrible outcome for the staff members who are increasingly the victims of violence, but as a result the young offenders aren't getting the best rehabilitation, which will have a knock-on affect on their future." 

Ms Wooldridge told The Age recently that since her government came to power in 2010, client-to-staff assaults had fallen 68 per cent and WorkCover claims among juvenile justice staff had dropped by 7 per cent.

''While in recent months there has been an increase in occupational violence WorkCover claims due to a particularly difficult client group, overall incidents have continued to decrease,'' she said.

She said the government had also significantly reformed the sector, including the introduction of 500 CCTV cameras, and the development of a special response team to support staff during serious incidents.

But the union spokesman said the Malmsbury special response team consisted of staff who usually worked at the centres' units and that this wasn't sufficient.

"When something happens they drop what they are doing and head over to assist the other staff with their unit's issues," he said.

"That leaves that person's unit short-staffed and the clients take advantage of those scenarios."

​He said morale was low in the centre.