The prison lockdown remains in force on Monday to ensure the safety of staff who are in on-site meetings and taking part in restricted work movements.

Victoria Police is now investigating the assaults.

The Community Public Sector Union is back at the centre to talk with staff, after a stop work order was issued, following the assault on the guards on Saturday.

"We have an agreement to implement ...stricter movement control and unit staff having the authority to lock down if (they) sense trouble," union representative Julian Kennelly told AAP.

If an agreement is not reached between the centre's management, the Department of Justice and prison union officials, the lockdown will continue until safety is guaranteed.

"Enough is enough. This is about getting control back at the centres," union secretary Karen Batt said on Sunday.

The centre has been plagued with acts of violence, with two guards hospitalised after separate attacks in July.

It comes about a month after a youth worker at Malmsbury Youth Justice Centre was allegedly bashed with a cricket bat and kicked, prompting a lockdown.

Australian Associated Press