Arsonists have lit 12 of the 68 fires burning across Victoria, with firefighters battling dangerous winds and conditions that are the worst since Black Saturday.

Fire Services Commissioner Craig Lapsley said the 21,000 hectare Grampians fire was so intense that it had “created its own weather”, triggering lightning and spot fires around Halls Gap.

Mr Lapsley said the southwesterly change, which will come through this afternoon, would increase the threat of bushfires raging through the Grampians, which have already killed one person.