UPDATE, 11.22AM: The fire has now been declared under control.
A quick response from air support, as well as ground crews, quickly helped contain the blaze.
EARLIER, 11.10AM: Fire crews are fighting an out-of-control grassfire near the Western Freeway.
At least five units are fighting the blaze at Bacchus Marsh, near the Avenue of Honour on-ramp.
There is a lot of smoke visible in the area.
Motorists in the area are advised to exercise extreme caution.
It is about 100 metres x 40 metres in size.
Air support has been requested.
There are not any structures under threat.