Motorists are being urged to drive carefully with a significant amount of fog in the southern suburbs.
Main Roads has advised there is reduced visibility on the Kwinana Freeway between Mundijong Road and Rowley Road.
Mandurah Road between Dixon Road and Rockingham Road has also been affected.
Drivers should switch headlights on, ensure a safe braking distance and allow for extra travel time.
A smoke alert is also current for Perth's northern and eastern suburbs, including the Perth CBD, in the Perth metropolitan area.
The smoke is the result of prescribed burns being carried out in Julimar State Forest and east of Dwellingup, as well as private property burning.
It is expected to clear by mid morning.
UPDATE: FOG OVER ROAD - AFFECTING SOUTHERN SUBURBS— Main Roads WA (@Perth_Traffic) May 12, 2019
Kwinana Freeway between Mundijong Road and Rowley Road
Mandurah Road between Dixon Road and Rockingham Road
REDUCED VISIBILITY IN THE AREA https://t.co/tZFEdtcok9 #perthtraffic