New South Wales fire crews battled the impact of wind gusts from a southerly change overnight after a challenging day that saw 300 new fires sparked in catastrophic conditions across the state.

Key points: 300 new fires flared on Tuesday in hot, windy conditions, but no lives were lost

300 new fires flared on Tuesday in hot, windy conditions, but no lives were lost A southerly change could fan fires tonight

A southerly change could fan fires tonight Conditions for Wednesday are expected to be cooler but authorities warn people to stay vigilant

The winds associated with a cool change moved north through the Greater Sydney and Greater Hunter regions around midnight and reached the north of the state, where a number of the emergency-level blazes were still burning.

As of 5:30am AEDT emergency warnings remained in place for two blazes among the 50-plus fires still burning around the state, down from 10 warnings shortly before midnight.

The two emergency fires were: Hillville Road in Hillville on the Mid Coast and Liberation Trail in the Clarence Valley.

Earlier, the state's Rural Fire Service (RFS) warned the southerly winds could see an increase in fire activity through the night.

RFS Commissioner Shane Fitzsimmons said firefighters fought 300 new fires in Tuesday's hot, windy conditions, and early estimates were that up to a dozen homes had been damaged or destroyed.

But he said no people were unaccounted for, a result he said was "most pleasing".

He said the state had benefited from the fact the earlier winds had not persisted for as long as initially forecast, and the existing smoke layer across northern NSW had served as an "insulation blanket" against encroaching winds.

Waterbomber called in to save Sydney homes

Sydney was dragged into the state's bushfire crisis on Tuesday afternoon when two emergency warnings were issued in a leafy suburb on the city's North Shore.

Two emergency-level bushfires were burning this afternoon just north of Macquarie University in South Turramurra, only 15 kilometres from the CBD, but were later downgraded.

A fire was burning intensely in bushland halfway between the university and Sydney Adventist Hospital before a water bomber dropped pink fire retardant over the area and turned several houses pink.

Mr Fitzsimmons said the "airplane was an urgent dispatch" and the pink colour was caused by a dye which could be easily washed off with water.

Several homes were damaged in the Turramurra blaze, adding to a toll of affected and razed homes across the state.

A house burning in Bora Ridge this afternoon. ( ABC News: Matt Coble )

Transport for NSW advised people to leave work early ahead of the southerly change that hit Illawarra about 5:30pm and hit Sydney at 7:30pm.

Trains were running under speed restrictions due to the heat as metropolitan Sydney was shrouded under a thick smoke haze.

Firefighters at the scene of the blaze in South Turramurra. ( ABC News )

The commissioner said there was no indication there would be catastrophic conditions tomorrow when cooler temperatures move in, but the public could "expect to see elevated fire dangers again".

A statewide total fire ban will remain in force however.

He added hot and windy conditions were forecast for Friday, Saturday and Sunday. But, at this stage, catastrophic conditions are not expected.

Firefighters battling the spread of the blaze at Turramurra. ( ABC News: Nick Dole )

'Complacency kills'

The day began with catastrophic fire danger warnings in place across the Greater Sydney, Greater Hunter, Illawarra and Shoalhaven regions, and more than 600 schools and TAFE campuses closed for the day.

Mr Fitzsimmons had started the day with a dire warning for millions of people living in the affected areas.

"Complacency kills. We cannot afford for people to be complacent," he said.

"The fact that that the catastrophic rating is there, that's the highest level risk available."

A man hosing down a burning tractor at Hillville. ( ABC News: Liv Casben )

While firefighters struggled at fire lines across the state, emotions boiled over in the state's north, where federal Opposition Leader Anthony Albanese and NSW MP Janelle Saffin were heckled at a press conference in Nimbin.

The Labor leader promised local fire crews he would lobby Parliament to provide all possible assistance to impacted communities.

"My house is burning down," a woman yelled.

"All my friends are out there, my whole life is out there, everything!"

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 45 seconds 45 s Angry residents unleash on Nimbin's local Labor member Janelle Saffin.

A firefighter collapsed after suffering from severe heat stroke and smoke inhalation while battling blazes in the state's wine country, where multiple homes were damaged.

Another firefighter was injured at the Turramurra fire and was being treated for a fractured arm and suspected fractured ribs.

Three properties were damaged by the blaze at Hillville, south of Taree.