Several bushfire warnings have been downgraded across Victoria, allowing locals in the Grampians to return home.

Authorities have growing concerns a large bushfire burning in the Grampians could spread rapidly on Boxing Day, fanned by strong winds and searing heat.

Two towns in the path of a rampaging bushfire have been told to evacuate immediately. Moyston and Pomonal residents in western Victoria were told to flee as the out-of-control monster blaze in the Grampians National Park bore down on them on Wednesday afternoon.