The violent escape of an immigration detainee, who remains at large, occurred just a week after new management took over a detention centre.

A search is under way across Sydney for the 28-year-old Tongan man who fled early on Thursday morning.

He was being driven from Villawood Detention Centre in Sydney’s west to Sydney Airport when the driver and passenger were attacked with a ‘sharpened metal object’ about 3.40am, police told reporters.

A 54-year-old man was stabbed in the neck and a 36-year-old man was assaulted during the attack.

The escape came shortly after Australia’s onshore immigration detention system was transitioned to new management.

US-based private prison operator Management and Training Corporation and its subsidiary Secure Journeys have been contracted to manage immigration detention centres until 2029 on a contract worth more than $2.3billion.

All centres were due to be transitioned from May 8, Australian Border Force deputy commissioner Vanessa Holben told a budget estimates hearing in March.

Centres in WA and the Northern Territory had already transitioned but Ms Holben did not specifically say when Villawood centre would transition.

Secure Journeys forwarded questions to Border Force, which said it did not comment on individual cases.

‘Any attack on workers carrying out their jobs is abhorrent,’ an Australian Border Force spokesperson told AAP.

‘The ABF supports all its staff and service providers, especially those who are subjected to abuse and assault while trying to do their jobs.’

The United Workers Union said members have raised concerns about unsafe staffing levels at centres nationwide since the transition.

‘Concerns about unsafe staffing levels extend to significant changes in how the detention network’s transport and escort team is operated and staffed,’ union official Godfrey Moase said.

‘Two officers are insufficient for this difficult and dangerous role.’

The detainee fled at Clyde with police dogs tracking him as heading towards Harris Park, Superintendent Simon Glasser said.

‘We are working closely with Australian Border Force and (the Department of Home Affairs),’ he said.

‘The victims are contractors who work for Villawood Detention Centre.’

The man is described as unshaven with a large build and is about 180cm tall. He was last seen wearing a dark jacket and pants and black and white sneakers.

He is known to police and frequents Mount Pritchard and other areas in southwest Sydney.

‘This was obviously a violent offence that’s occurred, so we do ask members of the public to be wary if they believe they see him and contact us, not to approach him,’ Supt Glasser said.

Both contractors were taken to Westmead Hospital but their injuries were not considered serious.

‘We have a lot of resources on this today to find this male,’ Det Sup Glasser said. 

‘We know that he frequents the Mount Pritchard area as well as other areas in western Sydney.’

An extensive search of the area is underway, with officers using police dogs to help track down the man. 

Police have warned the public not to approach the man if spotted and to instead call Triple Zero immediately. 

‘If anyone has any information or sees the male, please ring Triple Zero, or contact Granville Police or Crime Stoppers on 1800 333 000,’ Det Supt Glasser said.