Extreme fire danger is forecast for the Southern Ranges, Illawarra and ACT on New Year's Eve while surrounding regions - including Sydney, the Hunter and the far south coast - are set for severe fire danger.
Strong westerly winds are expected, pushing fires east and placing coastal communities under threat.
The NSW Rural Fire Service said bushfire-prone communities near Batemans Bay and Bega "should" move to large towns away from bushland by 8am.
Total fire bans are in place for more than half of the state's 21 fire districts including Sydney, while dozens of the state's near-100 blazes burn out of control.
In Sydney, strong dry winds, poor air quality and temperatures touching 33C are expected while the city's west will pass 40C.
Fire prediction maps suggest the Green Wattle Creek fire, which has already scorched 227,000 hectares, may cross the Hume Highway near Bowral, south of Sydney.
The Dunns Road fire near Tumut and the Badja Forest Rd fire near Cooma appear set to be among the blazes to expand most significantly.
Crews will also mourn a firefighter killed when the truck he was in crashed on Monday evening at the NSW-Victoria border town of Jingellic, about 70km east of Albury.
The RFS said its initial understanding was that the truck rolled under extreme winds due to the Green Valley fire.
Two male colleagues in the truck suffered burns and were taken to hospital.
A second truck was blown over, injuring one other firefighter.
NSW Premier Gladys Berejiklian tweeted that the death was "just heartbreaking" and "words fail at times like this".
Volunteer firefighters Geoffrey Keaton, 32, and Andrew O'Dwyer, 36, died on December 19 when a tree hit their tanker as they were travelling near Buxton, southwest of Sydney.
The Green Valley fire, which is also threatening communities on the Victorian side of the Murray River, was one of eight NSW blazes subject to either emergency warnings or watch-and-act alerts on Monday evening.
Near the Charleys Forest blaze - an offshoot of the massive Currowan fire - boarding kennel operator Matthew Knight is preparing to evacuate for the third time this season.
While usually the busy season, Rovers Retreat has been at less than half capacity this Christmas due to the need to evacuate quickly.
"We're all girding our loins for tomorrow because it doesn't look good," the Rovers Retreat manager told AAP on Monday evening.
He said he was mainly relying on messages via his landline and neighbours due to broadband and mobile network outages.
"Those apps (Fires Near Me), you rely quite heavily on them and when it goes a bit pear-shaped there's not even a mobile signal," he said.
Homes likely lost in Victoria
Homes and property are likely to have been destroyed by bushfires that have ripped through more than 200,000 hectares in Victoria's East Gippsland.
Seven emergency warnings, the highest alert, remain in place across the region and there is another in place for a fire straddling the northeast Victoria-NSW border at Corryong/Walwa.
The State Control Centre on Tuesday morning said towns, including Orbost, had been hit by the fire and impact assessment teams will be sent out to discover the extent of the damage.
Princes Highway is closed between Bairnsdale and Genoa. The fire has also crossed Great Alpine Road at Ensay, with people in the area warned mobile and landline phone coverage could be affected.
Many of the fires in the region have merged overnight.
A cool change swept through the region as expected after extreme heat on Monday, but windy conditions remain, further fuelling the fires and spreading ash.
More than 20 fires were still burning in Victoria on Tuesday morning, with the main focus of concern in East Gippsland and the northeast of the state.
A large uncontrolled fire moving from the NSW border prompted an evacuation alert for residents in Walwa.
A bushfire also threatened the northeastern Melbourne suburbs of Bundoora, Greensborough and Mill Park on Monday.
Lives and homes remain under threat while firefighters have battled the flames throughout the night in Bruthen, Lakes Entrance and Mallacoota
Town perimeter defences were breached by fires in Bruthen on Monday around 9pm, the CFA said.
Victorian Premier Daniel Andrews attended a briefing at the State Control Centre, cutting short his holidays to assess the situation on New Year's Eve.
There were no properties confirmed lost or damaged by the bushfires on Monday.
Conditions ease in South Australia
Cooler weather across South Australia will allow stressed Country Fire Service crews to get the upper hand on a number of bushfires.
Watch and act messages remain in place for fires on Kangaroo Island and on the Eyre Peninsula after catastrophic conditions on Monday.
But there have been no reports so far of property losses at either blaze and no further losses across the Adelaide Hills fire zone where the CFS is continuing to monitor the major blaze, which broke out 10 days ago.
More than 120 bushfires were sparked across SA on Monday, prompting the CFS to send more than 600 volunteers and 150 fire trucks into the field.
Chief Officer Mark Jones said the cooler conditions on Tuesday, with temperatures across much of the state falling to the mid-20s, would result in reduced risk.
However, he added, those fires still burning were large enough to sustain themselves for some time.
