Off-duty WA policeman 'savagely attacked'

An off-duty WA policeman who was bashed when he tried to catch three men on a crime spree is "barely recognisable", the police union says.

Police say the men first entered a bakery on Jarrah Road in Roleystone just before 9.30pm on Sunday and stole several items.

They then allegedly broke a glass panel on the front door of a bank before going to a nearby service station where they threw rocks and assaulted a fuel tanker driver.

The window of the truck was smashed and the driver had to lock himself in the tanker cabin for safety, police said.

The men then tried to break into the service station by smashing the front door.

An off-duty policeman, who tried to catch them as they ran away, is being treated at Royal Perth Hospital for multiple facial fractures and a broken nose.

WA Police Union president George Tilbury described the assault as horrific and savage.

"I am disgusted by the actions of the cowards who did this," he said on Monday.

"The offenders have left the senior constable with facial injuries so severe that he is barely recognisable."

Five men are being questioned by police.