POLICE have found a highway patrol car that was driven off by a man after he allegedly struggled with officers who pulled him over in Sydney's northwest.

Police are seeking a man called Arthur Partsch who they allege stole the car and they have warned the public not to approach him as he is considered dangerous.

The $120,000 patrol car was found parked in Parramatta at about 7.30pm (AEDT) on Sunday following a call from a local resident who realised it was the stolen vehicle after viewing media reports.

Police said Mr Partsch was driving along the M7 near Dean Park just before noon on Sunday when he was stopped by Traffic Strike Force officers.

Acting Superintendent Mark Cook said an officer from Mount Druitt also pulled up shortly afterwards because he knew the man.

When a struggle ensued, Mr Partsch allegedly broke free before hopping into a highway patrol car and driving off.

"I was told at the time it was raining," Acting Supt Cook told AAP, adding that conditions were "slippery".

It was "extremely rare" for such a car to be stolen, he said.

Mr Partsch is described as being of Pacific Islander appearance, 170cm tall, with brown eyes and a medium build.

Anyone who spots him should not approach him but contact police immediately.