Millions facing 'catastrophic' fire danger as Australian bushfires rage on

More than a dozen emergency bushfires are raging across NSW as millions of residents face "catastrophic" fire danger with a southerly wind change expected to make matters even worse.

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More than 3000 firefighters are battling the blazes, which officials warn are catastrophic and life-threatening. Source: 1 NEWS

Almost 80 fires are burning from near Nowra all the way up to the Queensland border.

Some 50 bushfires are uncontained and authorities say there's no let-up in sight as a southerly change sweeps up the state threatening to spread the fires even further.

"We are still concerned with the movement of the southerly change as it heads through NSW over the coming hours," Rural Fire Service NSW commissioner Shane Fitzsimmons told reporters in Sydney.

There were 15 fires at emergency warning level today at 5pm including one at South Turramurra on Sydney's upper north shore.

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1 NEWS was there as the team of 21 set off, following an offer from PM Jacinda Ardern. Source: 1 NEWS

That blaze has subsequently been downgraded to "advice" level.

There are reports of firefighters across the state suffering injuries including heat stroke and fractured bones.

The 15 fires at emergency warning level include blazes in Sydney, the Hunter northwest of Newcastle, Taree and surrounds, inland from Port Macquarie and Torrington north of Glen Innes near the Queensland border.

A fire in North Rothbury, near Cessnock, this afternoon was also elevated to emergency level.

There are reports of damage to multiple homes in that area, Mr Fitzsimmons said, as well as impacts to a number of structures in the Hillville area south of Taree.

Mr Fitzsimmons said the southerly change would reach Sydney by 7pm and hit the north of the state later today or early tomorrow morning.

"We simply can't rest easy at this stage. We've got many hours left yet of prevailing, hot, dry, windy conditions," he said.

Mr Fitzsimmons said the day was unfolding as predicted with a million hectares burning.

He thanked people for following the advice of the RFS in using the Fires Near Me app to monitor where the danger was.

The app has been opened more than 4.2 million times in recent days.

Bureau of Meteorology state manager Ann Farrell says as the southerly change moves up NSW "the fires will be fanned in a different direction".

"They'll be very gusty and quite unpredictable at times - so that will make fire conditions much more dangerous," she told reporters in Sydney.

More than 3000 firefighters and 80 aircraft will potentially be involved in battling the blazes.

Premier Gladys Berejiklian urged residents to heed warnings and head for safety.

"We need to make sure every community member takes the opportunity to assess the situation and act with precaution in every possible manner," she said.

A catastrophic fire danger rating - the highest possible - is current for the Greater Sydney, Greater Hunter and Illawarra-Shoalhaven regions.

Temperatures in the high 30s, low humidity and winds gusts beyond 70km/h coupled with drought mean the state faced "horrendous conditions", the RFS said.

A week-long state of emergency has been declared in NSW with the armed forces standing by to provide support, including for search and rescue operations.

Some 600 schools were closed today.

The bushfires, which hit hard on Friday, have claimed three lives and destroyed at least 150 homes so far.

The RFS has received 1500 emergency calls to their operations centre since this morning.

They urged people not to call triple zero except in emergencies. Residents should rather use the app to keep updated on where the fires are spreading.