A police car destroyed by fire west of Brisbane appears to have been accidentally driven down a ditch rather than "parked" by the side of the road as originally stated.

A witness to the intense fire said the police officer pulled over a speeding motorbike rider at the intersection of Wivenhoe-Somerset Drive and Northbrook Parkway near Mount Glorious but when the bike took off again, it looked like the officer tried to give chase.

"Next minute the bloody cop car drives down the bank," truck driver David Hunn said.

Queensland's police operate under a strict pursuit policy, which prevents them from giving chase in all but the most extreme circumstances.