MONDAY, 7.10am: A prison source said three prison officers were punched and kicked by inmates.
The guards required medical treatment, one for serious facial injuries, after the attack.
One of the men was treated at the scene, while another man, in his 30s, was transported to the Bendigo hospital in a serious but stable condition.
It is understood about five detainees were involved in the brawl.
The entire secure unit housing about 45 youths went into early lockdown and will remain that way until Monday morning.
A prison source told Fairfax Media the fight was instigated by a recent assault on a female staff member by a detainee.
The source said two of the inmates wanted to access another detainee, believed to have attacked the woman days ago but when officers intervened a fight broke out.
The group of detainees also smashed windows and a camera during the fight.
The fight is the latest in a string of violent incidents at the troubled youth justice centre.
In January, a group of six inmates escaped the facility and stole three cars before being arrested by police.
SUNDAY: Police and emergency services are again attending the Malmsbury Juvenile Justice Centre following reports of a group of youths causing trouble.
A Victoria Police spokesman said it was believed a number of youths assaulted up to three staff members and caused damage to the centre at about 2.45pm.
One staff member will be treated for a facial injury.
An Ambulance Victoria spokesman confirmed paramedics were called to a report of an assault.
Police are investigating the incident.
- with The Age