Bushfires threatening homes on the NSW south coast in winter have left scientists "gobsmacked", while warning communities to prepare for worse to come.
Scientists are "gobsmacked" that out-of-control bushfires are burning on the NSW south coast during winter, leading to a total fire ban across much of the state.
Equally troubling, one expert says, is global warming means the northern and southern hemisphere fire seasons are overlapping, which is stretching global firefighting resources.
"We're seeing something which is unusual in the extreme," environmental change academic David Bowman told AAP on Wednesday.
"It's worrying, it's mind-bending.
"We've got the largest fire complex burning in San Francisco and fires burning in the Glacier National Park on the Canadian border, which we've just sent crews to, and now we have this extreme weather fanning NSW fires in winter."
At least 30 fires were burning out of control in NSW on Wednesday, with homes and lives threatened by the most serious blazes at Mount Kingiman and North Nowra.
Professor Bowman, of the University of Tasmania, says many people are not aware bushfires can run riot without extreme heat if strong winds and enough dry fuel are present.
Those are the types of conditions likely to increase due to climate change.
"The trajectory we're on, we know these extreme events are going to increase," Prof Bowman said.
"There's an expectation that new technology can put any fire out so people want to see it used more, without any idea of the cost.
"We're spending more and more on fighting fires. The fires in the western US are going to cost multiple billions of dollars."
Bushfire safety researcher Jim McLennan says he's "gobsmacked" to see so many fires in winter.
Proactive fire prevention had suffered a lack of government funding, the La Trobe University researcher told AAP.
"Cash-strapped local governments not mitigating risk can create a real problem," he said on Wednesday.
Dr McLennan recommends homeowners should always create clear zones around their property.
"Then again, if the wind is sufficiently strong, it's going to burn no matter what you do," he said.
"Unfortunately, people are going to have to stop thinking of these as rogue events and start thinking of them as the new normal."
A total fire ban is in place for the greater Sydney, Hunter Valley and Illawarra regions until midnight on Wednesday.