Easing conditions Sunday after a week-long heatwave helped Australian fire crews battling major wildfires that destroyed 25 homes in the southeast, but there were warnings of a long and dangerous season ahead.

Firefighters in the states of South Australia and Victoria said they had gained the upper hand over a series of blazes which started last week during temperatures of more than 40 degrees Celsius (104 Fahrenheit) for several consecutive days.

Fires in South Australia levelled 15 homes, while Victoria's Country Fire Authority said a firestorm -- so intense that it created its own weather system in the Grampians holiday park west of Melbourne -- had destroyed at least 10 properties.

One woman died in the Grampians, although authorities said it appeared to be due to a medical condition and not fire-related.

An eleventh-hour wind change spared the town of Halls Gap, where more than 100 people had evacuated their homes as the fire-front approached, said Victoria fire commissioner Craig Lapsley.

"Halls Gap dodged a bullet," he said.

Residents in the popular tourist area described the dramatic wind change coming through.

"All of a sudden, bang, the wind turned, the waves started coming down the lake and what looked like red all of a sudden turned to blue sky," said Rohan McDonald, owner of the Halls Gap Lakeside Tourist Park.

Lapsley said crews had "done reasonably well" to limit property damage and casualties in what had been the worst conditions since the so-called Black Saturday fire disaster which killed 173 people in 2009.

"We've had big fires, 100,000 hectares (247,000 aces) burnt in a manner of basically two days," he said.

In South Australia there were still five major blazes but cooler and less windy conditions helped containment efforts overnight.

Lapsley said there was no room for complacency, with dangerous conditions forecast to continue until March.

"This is the start or the changing point in this summer," he said.

"We don't see any rain, we don't see the break in the weather and we certainly see warm conditions for the month of February."

Emergency Services Minister Kim Wells echoed fire authority warnings.

"The bushfire season has only just commenced and it is important that anyone who lives or works in a bushfire-prone area remains vigilant and ensures that they have a bushfire plan in place," he said.

In New South Wales, spared the worst of last week's heatwave, there were unconfirmed reports that some homes had been destroyed by fresh blazes in the state's southwest started by lightning early Sunday.

"There are reports of property losses. However, due to dangerous fire conditions, firefighters are unable to enter a number of fire-affected areas," the Rural Fire Service said.

The village of Carabost, with a population of about 150, was being evacuated as 40-metre (132 feet) flames moved towards properties from a blaze in the Murraguldrie State Forest near Wagga Wagga.

In October more than 200 homes were destroyed and two lives lost in a NSW fire emergency west of Sydney -- unseasonably early for wildfires, which are common in Australia's summer months of December to February.

One week ago a fast-moving wildfire razed 56 homes on the outskirts of Perth on Australia's west coast, under sweltering heat that spread across the continent to the southeast.

Experts say heatwaves are becoming longer and more frequent in Australia due to climate change.