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
Cooloongup man accused of historical child sex offences dies just weeks before trial
Boat owners urged to make safety a priority this Easter
Mundijong man accused of attempting to procure children overseas for sexual activity
PM Anthony Albanese to address nation
Mandurah teacher who raped student to remain on bail
Man charged after allegedly exposing himself to girl on Transperth bus in Lakelands
Fire rips through Golden Bay home
Firefighters battle bushfire near Nambeelup
Alcoa Children's Festival cancelled due to severe weather