Four homes were destroyed as Australian firefighters struggled to bring two major blazes under control in Victoria state with high temperatures and gusty winds ahead of a cool change later Thursday.

Lightning strikes this week ignited 350 fires with several becoming significant, according to authorities. Some 500 firefighters are tackling the outbreaks with nearly 10,000 hectares (24,700 acres) razed.

Two fires in Victoria's northeast -- at Lake Rowan-Warbys some 20 kilometres (12 miles) northwest of the regional city of Wangaratta and Creightons Creek-Longwood just south of Euroa -- have been burning for several days and remain out of control.

"There have been four confirmed house losses but we're still assessing the extent of the impact on agriculture," Victoria's Country Fire Authority spokesman Lee Miezis told AFP.

"We do understand that one farmer has lost about a thousand head of stock, so it's quite a significant impact on stock."

Officials late Thursday downgraded an emergency warning for communities around Mia Mia, Meadow Valley and Glenhope in central Victoria after containing the spread of a fast-moving grassfire.

The weather conditions were set to remain challenging ahead of a forecast drop in the temperature in the evening.

"As that cold change moves across the state, we are starting to see some stronger winds from the southwest with the wind speed getting up to about 40 kilometres an hour (24.9 miles per hour)," Miezis said.

"The winds are switching from the west to the southwest and are getting stronger."

The cooler weather and lighter winds will allow firefighters to strengthen their control lines, put out burning trees inside fire areas and get the blazes under control, he added.

Control lines involve removing vegetation that fuels fires, using equipment such as bulldozers or rakes.

Backburning, a tactic aimed at managing the path of a fire by starting a controlled new blaze in the opposite direction, is also used.

Firefighters have had difficulty putting in control lines as the northeast blazes were burning in "quite scrubby, rocky, steep country", Miezis added.

He said southeastern Australia looked set to experience an above-normal fire season after an unseasonably dry spring.

"With that dryness, we've had quite a lot of vegetation dry and there's no real moisture in the soil," he said.

"In simple terms -- a long, hot summer and probably about 12 weeks of increased fire danger."

Wildfires are common in Australia's summer months between December and February.

"Black Saturday", the worst firestorm in recent years, devastated southern Victoria in 2009 as it razed thousands of homes and killed 173 people.