A second fire in two weeks ripped through Bold Park reserve in Mt Claremont yesterday, sparking an investigation by the arson squad.
People were urged to evacuate as firefighters battled to control the blaze in the popular bush reserve.
A Fire and Emergency Services Authority spokeswoman said the fire started between Rochdale Road and West Coast Highway and was reported by a triple-zero caller at 4.06pm.
She said there had been heavy smoke in the area.
Another blaze in Bold Park on March 17 was deliberately lit and came within about 400m of homes.
Det-Sgt Chris DeBruin said the arson squad would investigate yesterday's fire, and they could not rule out a firebug being responsible.
A fire in Koondoola on Wednesday that threatened homes was also being treated as suspicious.