Thousands of Australians were told to leave their homes as dry winds created the conditions for a firestorm in mountainous bushland outside Sydney, where firefighters have battled for days to bring dozens of wildfires under control.
More than 200 homes have been destroyed in New South Wales state since last Thursday, when bushfires tore through scattered communities to Sydney's south and west, razing entire streets.
One man died after suffering a heart attack trying to protect his home.
Wednesday's fire conditions were shaping up to be the worst so far in the state's bushfire crisis, said Shane Fitzsimmons, the commissioner of the rural fire service.
"If you don't have a plan, let me give you one," said Michael Gallacher, the state's emergency minister. "Get into the car, drive down to the city metropolitan area and let the firefighters do what they can do to protect the community, should this turn for the worse."
Temperatures in the Blue Mountains west of Sydney are expected to reach up to 30C, while in Sydney itself they could hit 35C. Hot, dry winds gusting up to 100km/h are also expected, posing the greatest challenge to firefighters.
"This is the day where we've been receiving forecasts of the worst of weather for this week and that forecast is still staying with those predictions," Fitzsimmons told reporters, warning of extreme fire conditions.
Al Jazeera's Jonathan Gravenor, reporting from Katoomba's Rural Fire Service, in the Blue Mountains, said there were more than 3,500 firefighters still battling fires in the region.
There were still 60 fires burning across the state on Wednesday, with 18 out of control, our correspondent said.
Authorities ordered schools in the Blue Mountains to be closed, evacuated nursing homes and advised people living in the area to leave before conditions deteriorated.
The Blue Mountains, whose foothills extend down to western Sydney suburbs such as Penrith, are populated with a mix of farmers, small business owners and white-collar commuters who make the trip into the city every day.
Known for their spectacular escarpments, eucalyptus forests and scattered small communities, they are a popular tourist spot for Sydney residents on weekends.