A number of homes in south Manchester were evacuated as two police vehicles were completely destroyed by fire.
The liveried vehicles - a Ford Transit van and Ford Fiesta - were found on fire in a police car park in Didsbury in the early hours of Saturday.
Another Transit van had minor damage although nobody was injured in the blaze near Davenfield Grove.
Forensic examinations of the scene are continuing and Greater Manchester Police have appealed for witnesses.
A spokeswoman for the force said: "It is not clear at this stage what caused the blaze."
Nearby residents were allowed to return to their homes a short time after the fire at 0500 BST.