A volunteer firefighter has died and two others have been injured while working on a fire burning near Albury, the NSW Rural Fire Service (RFS) has confirmed.

Key points: All three firefighters were working on a blaze near Jingellic, 70 kilometres east of Albury

All three firefighters were working on a blaze near Jingellic, 70 kilometres east of Albury It follows difficult conditions in which some fires generated dangerous thunderstorms

It follows difficult conditions in which some fires generated dangerous thunderstorms Temperatures hit the low 40s in some parts of the state, with worse expected tomorrow

The RFS said the three firefighters were the same truck working on a blaze near Jingellic, near the Victorian border, when it rolled over after being hit by extreme winds.

One firefighter was killed and two others suffered burns and were taken to hospital.

A second vehicle working on the same fire was also blown over and the firefighter on board was taken to hospital, the RFS said in a statement.

"The service's thoughts are with all the firefighters' families, friends and fellow brigade members," the statement said.

It followed another day of bushfire danger, with strong winds and soaring temperatures fanning flames towards major population centres.

Two fires are burning at emergency level, including the Green Valley, Talmalmo fire in the Greater Hume area, and the Werri Berri fire in the Bega Valley.

The NSW Rural Fire Service (RFS) tweeted that a fire-generated thunderstorm had formed over the Badja Forrest Road and Turross Falls Road fires, which were burning north-east of Cooma at watch and act and advice levels, respectively.

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Total fire bans were declared in 10 areas on Monday, including the Illawarra, Hunter and Greater Sydney, but conditions tomorrow are expected to be even worse.

The temperature at Penrith, in Sydney's west, has been forecast to reach 40 degrees Celsius on Monday and 44C on Tuesday.

Regional areas are also expected to swelter on Monday, with Wagga Wagga (42C), Hay (44C), and Wentworth (45C), among the hot spots.

The RFS is particularly concerned about the massive "mega-blazes" at Gospers Mountain and Green Wattle Creek, which have encircled Sydney.

The Bureau of Meteorology said a front moving through south-eastern Australia is behind the difficult conditions.

There is a risk of dry lightning, as well as strong, gusty winds as a mass of hot air settles over the state.

"That hot air is coming out of the centre of Australia, it's particularly dry and then unfortunately conditions are expected to worsen in New South Wales as we head into Tuesday," RFS Commissioner Shane Fitzsimmons said.

"The winds are expected to strengthen up on average to 50, 60 kilometres an hour and potentially gusting 70 to 80 kilometres an hour."

The "mega-blaze", which includes one at Gospers Mountain, has encircled Sydney. ( AAP: Dan Himbrechts )

Yesterday, the RFS continued large backburning operations around Sydney and warned residents in several areas to be prepared as conditions deteriorated.

Tom Grant and his wife Rachel built their home near Hill Top, about 115km south-west of Sydney's CBD and 75km from Wollongong, two months ago.

They're not taking any chances and evacuated at the weekend after crews warned the Green Wattle Creek blaze was expected to reach the town this week.

"We have a three-week-old baby and a one-year-old so our priority was to get them out," Mr Grant said.

"Luckily, our house is so new it's got the highest safety rating possible."

Tom and Rachel Grant had plenty of important cargo to consider as they evacuated. ( ABC News: Jake Lapham )

Almost 900 homes have been razed, and 3.48 million hectares of land has been burnt in NSW so far this fire season.

In Victoria, the fire danger in several regions was rated "extreme" on Monday.

The entire area of East Gippsland — a popular holiday destination — was yesterday urged to evacuate and the Falls Festival at Lorne was cancelled.