Adelaide low-security prisoner Shane Gauci is still missing after he used a toilet break at an On The Run service station to go on the run from police yesterday.

Police allege the 41-year-old fled from a prison bus about 8:30am on Monday during a petrol stop on Gorge Road at Newton — north-east of Adelaide.

The service station on Gorge Road — between Rasheed Avenue and Jan Street — is close to Newton Central shopping centre.

The Department for Correctional Services confirmed yesterday morning that the prisoner had escaped and said a search operation was underway in the Newton area.

The spokesperson said the prisoner had made the escape while taking part in a community program which pre-release prisoners were eligible for.

"A police operation is underway to locate a prisoner who is currently unlawfully at large," a spokesperson said.

The prison bus which a man escaped from at Newton in Adelaide's north-east. ( ABC News )

"The prisoner became unaccounted for this morning while participating in an external work program as part of his accommodation at the low security Adelaide Pre-release Centre (APC).

"The [APC] plays a critical role as a rehabilitation and reintegration facility for prisoners preparing for release back to the community.

"Low-security prisoners at the [APC] are eligible to participate in community work programs following stringent and thorough security assessments prior to and during their participation in these programs."

The department spokesperson said the search operation had now been handed over to South Australian police and there had been no confirmed sightings of the prisoner at this stage.

Police at an On The Run petrol station in Newton where a prisoner escaped a transport van. ( ABC News: Simon Goodes )

Witness Khoo Phiesert Chanthapanya said the prisoner could have disappeared easily because he was wearing a fluoro vest.

"A lot of people came in this morning wearing high-vis vests and they could have blended in with everyone else. It was a busy time of the morning," he said.

"It's a pretty good time for him, I guess — a busy time to walk away. You know, everything is happening at the same time."

SA Police and the Corrections Department released Shane Gauci's details on Monday night.

"Shane Gauci had been on the bus travelling on Gorge Road Newton with Corrections officers when it stopped at a service station," a police statement said.

"He did not return to the Department of Corrections bus that was transporting him on a pre-release work program ... and is now unlawfully at large."

He is described as Caucasian, 180cm, 95kg, with brown hair. He was last seen wearing a blue t-shirt, khaki pants and black boots.

Police said Shane Gauci should not be approached and anyone who sees him should call 131 444 immediately.