Perth residents are waking up to smokey conditions as the effect of fires north-east of the city are felt across the metropolitan area.

An alert from the Department of Fire and Emergency warned people in the Perth CBD and greater metropolitan area of significant smoke blowing in from prescribed burning and private burns.

The smoke is expected to linger for a couple of days before clearing.

There are active planned fires in Gidgegannup, Darlington and Chidlow, and a bushfire burning in Lexia, about 20km north of Perth.

Motorists are urged to reduce their speed and turn on their headlights. If visibility is blocked, drivers should pull over, turn on their hazard lights and wait for the smoke to clear.

DFES has also issued advice to shut doors and windows and turn off air-conditioners. People with asthma and pre-existing respiratory or cardiovascular illnesses should follow their pre-prepared treatment plan.