There has been a mass escape from the Malmsbury Youth Justice Centre in central Victoria, with seven inmates on the run after stealing several vehicles north-west of Melbourne.

Key points: Seven inmates are on the run after escaping from Malmsbury Youth Justice Centre

Seven inmates are on the run after escaping from Malmsbury Youth Justice Centre Five inmates were seen on the roof of the complex

Five inmates were seen on the roof of the complex Witnesses reported cars driving erratically at speeds up to 100kph

Superintendent Craig Gillard said about 30 inmates were involved in a disturbance at the centre about 2:45pm and that 15 youths had escaped the facility.

Six of the 15 were arrested soon after the escape and two more were captured in a paddock 5 kilometres from the centre on Wednesday evening.

Sorry, this video has expired Police give an update on the Malmsbury escapees

Superintendent Gillard earlier reported three cars had been stolen since the incident and were believed to have been used by the escapees.

Police have since ruled out a red hatchback as being involved in the incident.

A white Suzuki SUV, which several escapees had been travelling in, was involved in a collision with another vehicle and dumped at the intersection of Springvale and Wellington roads in Mulgrave about 11.40pm on Wednesday night.

The occupants have fled the scene and it is not known whether they are now in another vehicle or on foot.

A number of escapees are also believed to be travelling in a blue Ford Falcon sedan, with registration ZKV598.

Five inmates also climbed on the roof of the complex during the disturbance. Police said there had been no reports of injuries.

One witness said she was driving along the Calder Highway at Lockwood South when a car carrying about six young people coming in the opposite direction swerved at her car, forcing her off the road.

"The police stopped the car probably about 100 metres past us and forced the car off the side of the road," caller Sandra told ABC Statewide Drive.

"There's probably seven or eight police cars there, the people are out of the vehicle and I believe they [the car] may have hit one of the police cars."

Police said its operations response unit, the dog squad and local police were on the scene.

Car travelling 'like a bat out of hell'

Wendy Taylor said she was driving through the main street of Castlemaine with her granddaughter when a little red car sped "like a bat out of hell" through a roundabout travelling about 100 kilometres per hour.

"This was a roundabout, but he didn't look in any direction at the roundabout, he just went straight through at major speed," she said.

"It was extraordinary, everybody looked around to see who was pursuing him, but there was actually nobody at all behind him.

"[I've] never seen anything like it before."

She said the car was driven by "one guy", with no obvious passengers.

Authorities have urged the public to stay away from the area and to call Crime Stoppers if they see anything, or dial triple-0 if they are in immediate danger.

Police gather near a fence of the Malmsbury Youth Detention Centre after inmates escaped. ( ABC News )

Escape 'not surprising' former officer says

It is the latest disturbance following months of unrest in Victoria's youth detention system.

Earlier this month, a disturbance at the centre was brought under control after a group of inmates locked themselves in a secured section and armed themselves with poles.

Greg, a former Malmsbury prison officer who retired last month, said he was not surprised by the incident.

"Having worked at Malmsbury, it's not surprising. There has been a number of riots at Malmsbury over the last 12 to 18 months," he told ABC Statewide Drive.

"I was assaulted and knocked unconscious by three youths during a riot in March, and I had my keys and swipes taken."

He said the prison was short-staffed, leaving officers vulnerable.

"On the one hand the youth become very highly destructive and unruly if they're on lockdown for long periods of time," he said.

"But if you don't have enough staff, you have to place these youths on lockdown.

"It's a double-edged sword, when these youths are allowed out of their rooms, you have to make sure that there's sufficient staff and at times there's not and so staff are left in a very dangerous and vulnerable position."

State Opposition Leader Matthew Guy said Victoria's reputation was being destroyed by a crime wave and Premier Daniel Andrews was "missing in action".

"What is happening to our state?" he said.

"It is completely and utterly outrageous to see what is happening on the Calder Highway … this appears to be a law and order crime wave that is beyond the Premier."