Help on the way ahead of catastrophic fire forecast

Specialised firefighting teams are among the 100-strong interstate personnel being sent to Victoria ahead of catastrophic conditions forecast for a region under continued threat.

Heavy rain in Melbourne has done little to quell major bushfires burning across 41,000 hectares in the Grampians in Victoria's west.

Millions of residents and travellers across the country are being warned to stay alert as the risk of Christmas week infernos intensifies.

Several states entered Monday battling dangerous blazes or warning of potential outbreaks, including NSW where hot, dry and windy conditions pose an extreme fire danger in the Greater Hunter, Greater Sydney, Northern Slopes and North Western regions.

Temperatures in the Victorian capital will peak at a cool 18C on Monday, with further showers expected.

"We did see some rain move across parts of the state overnight that hasn't had a significant effect on most of our fires," State Control Centre spokesman Luke Hegarty said.

"Realistically, for a fire like the size of the Grampians fire, we'd be needing significant amounts of rainfall, and that's not what we saw."

A watch and act alert remains in place for fires in the Grampians National Park and some residents have been told to prepare to leave if the situation worsens.

Catastrophic conditions are forecast for the area on Boxing Day, with temperatures predicted to reach about 40C and fears private property could be impacted.

More than 100 personnel will be sent from NSW, the ACT, Queensland and Tasmania to help with the fires, including two incident management teams and four specialised firefighting taskforces.

"A bit of support will be much appreciated by our crews, particularly given the time of the year," Mr Hegarty said.

Another blaze in Bullengarook, northwest of Melbourne, continues to burn out of control but is at an advice level warning.

With Boxing Day usually a big travel day across the state, authorities are urging residents to download the VicEmergency app before they leave.

Halls Gap Hotel, in the Grampians' biggest tourist town, has shut its doors and tourism providers in the area say they face losing $1.9 million a day in bookings because of the emergency as residents fled to Ararat.

Elsewhere, regional areas in South Australia are also expecting hot conditions on Boxing Day, with Adelaide facing a peak of 36C after a predicted 37C on Christmas Day.

In WA, firefighters were mopping up a blaze on Sunday that had threatened life and property on Perth's northern outskirts.

The fast-moving fire at Two Rocks forced evacuation warnings on Sunday afternoon but was later brought under control.

High fire danger is again forecast for the region on Monday while extreme risk is predicted in inland parts of WA's midwest and southwest.