A bushfire warning has been issued for residents north of Perth as the smoke cloud from the out-of-control blaze continues to blanket the city.
A watch and act alert has been issued for residents in and near Mundaring Weir Village, near Mundaring Weir Road between Firewood Road and Lockwood Road, in the Shire of Mundaring and City of Kalamunda.
The Department of Fire and Emergency Services is warning people to leave or get ready to defend their property as the fire moves quickly towards Mundaring Weir freshwater reservoir.
It is suspected the fire was deliberately lit at about 8.30am on Sunday about 12km south of the Mundaring township in the Perth Hills, DFES said.
It has burnt through more than 1000 hectares including pine tree plantations.
Aerial water bombers are assisting 150 Parks and Wildlife Service, DFES and volunteer firefighters to battle the blaze and build containment lines. They are expected to work through the night as they try and contain the fire.
A low pressure system following ex-Tropical Cyclone Joyce is trapping smoke over Perth, with reports of ash falling in suburbs as far apart Leeming and Hamilton Hill.
The smoke plume is so big it can be seen from Rottnest Island more than 65km away.
Roads have been closed, as well as part of the popular Bibbulmun Track and motorists are being asked to avoid the area.
St John's Ambulance has advised people to stay cool and avoid being exposed to smoke.