Thousands of firefighters fanned out across eastern Australia Tuesday as gale-force winds, scorching temperatures and tinder-dry bushland brought "catastrophic" fire conditions.

Dozens of bushfires were already burning out of control as temperatures were expected to climb toward 40 degrees celsius (104 Fahrenheit) and winds were forecast to top 60 kilometres (40 miles) per hour in parts of New South Wales.

Firefighters warned the threat to a vast region surrounding Sydney was "off the scale" after days of blazes that have killed three people and destroyed more than 150 homes.

New South Wales Rural Fire Service Commissioner Shane Fitzsimmons warned that in current conditions, "if a fire starts and takes hold... we are not going to stop it."

"We have already got significant fires burning in the north coast of New South Wales. A number of those fires are exceeding 100,000 hectares alone. You're talking about a 1,000-kilometre fire perimeter."

West-to-east winds threatened to spread existing blazes from drought-stricken bushland to population centres on the coast.

Up to 600 schools were closed, as well as many national parks, a total fire ban was introduced and residents in several areas were told to consider getting out.

The police and military were helping firefighters with logistics and running water-dropping sorties using more than 80 aircraft.

"Now is the time to exercise those decisions to leave, leave early and go to safer locations," said Fitzsimmons.

In the small northern town of Taree, dozens of people moved to a showground that has become a makeshift evacuation centre.

Fifty-nine-year-old Caroline Watson arrived last night with her husband and their dog.

"The fires are just rife. They are absolutely everywhere" she told AFP. "They didn't ask us to get out, but we figured it was coming."

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Australia's 'catastrophic' bushfires
The town of Taree, 350 kilometres north of Sydney, was readying for "catastrophic" fire conditions. Photo: AFP / PETER PARKS