A flame-haired woman has firebombed a police station in Perth's northern suburbs in broad daylight.

A woman with dark red hair was witnessed throwing a molotov cocktail at Wanneroo Police Station on Friars Drive around 7.30am (WST) on Wednesday as she rode past on a bicycle.

Damage to the front of the building was minimal, police said.

They are conducting patrols of the area in a bid to find the woman.