Firefighters are battling an out-of-control bushfire about 65 kilometres north-west of Melbourne.


Thirty-two trucks and two aircraft are at the medium-sized fire at Riddells Creek, near Mount Macedon.


The fire in the Mount Charlie Road area broke out about 4.30pm and is heading towards Romsey, although no homes are currently under threat.


A watch and act warning has been issued for Cherokee, Kerrie, Romsey and Riddells Creek.


"The outlook is looking more positive in the last few minutes," Country Fire Authority spokesman Gerard Scholten said. "We're relatively confident that we will be able to bring it under control fairly soon."


Residents have been asked to follow their bushfire survival plans. Those who are away from their homes have been advised not to return to the area.


Drivers have been warned to turn on headlights and drive slowly due to smoke affecting visibility.


Meanwhile, residents in Arthurs Creek, about 45 kilometres north-west of the city have been warned that a small, fast-moving grassfire is heading towards them.


Mr Scholten said the fire in the Brennans Road area was not threatening homes or properties.


"It's putting up a bit of smoke…so we're asking communities to be alert and vigilant and keep listening to emergency broadcasters," he said.