Steep, rocky terrain is hampering efforts to control the spread of a 9,000 hectare bushfire in the Grampians, in western Victoria.

Cooler temperatures initially offered some respite to firefighters and residents after three bushfires merged into the one huge fire in the Victoria Valley, north of Dunkeld yesterday.

The out-of-control blaze threatened homes at Mirranatwa, before a southerly wind change last night pushed it back into the Grampians National Park.

The fire is now burning in a westerly direction in the Victoria Range near the Glenelg River and creating spot fires.

Incident controller Paul Bates says it will be difficult to get bulldozers and ground crews into that area.

"We're going to have to have a good think about how we go about putting containment lines around that," he said.

A watch and act message has been issued for the communities of Woohlpooer, Glenisla and Mooralla, where the fire could impact anytime in the next four hours.