NSW faces its greatest bushfire threat - premier

Thousands of firefighters are on alert as New South Wales prepares to face what's expected to be its worst bushfire danger in history.

Temperatures well into the 40s and fresh winds are predicted for Tuesday.

The ABC reports areas on the state's south coast are the most in danger and a total state-wide fire ban was imposed in New South Wales from midnight on Monday.

The fire danger in the Illawarra, Shoalhaven and southern ranges is expected to be catastrophic, with many other areas expecting extreme danger levels, the ABC reports.

Premier Barry O'Farrell says record rains have produced large fuel loads which increase the risk of fire, combined with record temperatures and high winds.

"Tomorrow is not going to be just another ordinary day," he said on Monday.

"Tomorrow will be perhaps the worst fire-danger day this state has ever faced."

More than 90 fires are burning across the state and firefighters are battling to contain around 20 of those which are still out of control.

Thousands of firefighters and about 70 aircraft have been placed on standby.

The Rural Fire Service (RFS) at one point urged residents in the village of Oura, to the north east of Wagga Wagga, to consider evacuating due to an uncontrolled 870 hectare grass fire.

Regional fire manager Roger Orr scrambled a skycrane water bomber from Wagga Wagga airport to fight the fire, and later said the threat had eased.

A firefighter has been treated for minor burns after a ground-based tanker was overrun by fire near the village, but the rest of the crew were unharmed.

And another firefighter was burned and his truck badly damaged while battling a 76ha grassfire near Gunning, north of Canberra.

In the state capital, Mr O'Farrell has warned Sydneysiders they will not be spared from the heat.

"If Sydney reaches 43 tomorrow, it will only be the third time in the history of record keeping that the temperature in Sydney has been that high," he said.

The Premier says people must have their bushfire survival plans in place, as complacency could cost lives.

In the adjacent Australian Capital Territory, firefighters are bracing for the worst fire conditions in 10 years, while a fire burning in south west Victoria has destroyed 4000 hectares.

Rural Fire Service (RFS) Commissioner Shane Fitzsimmons says people should be alert to any danger.

"They need to monitor their local conditions," he said.

"They need to listen to radio, they need to watch TV, they need to refer to the website, they need to access social media tools such as Facebook and Twitter, do not rely on one source for all your information."

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