A fog warning is in place for parts of Pinjarra, Ravenswood and Mandurah.
The warning is also in place on the Kwinana Freeway from Mortimer Road to Pinjarra Road.
The fog is particularly strong on Pinjarra Road between Ravenswood and Mandurah.
Drivers are advised to turn their headlights on, allow a safe breaking space and drive with caution.
UPDATE: The fog warning has now been cleared.
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