Video report by ITV News reporter Helen Keenan
It brings the number of firefighters killed to 10.
It said the firefighter died near Jingellic, a town on the state border with Victoria around halfway between Sydney and Melbourne.
Two further firefighters suffered burns when the truck all three of them were in rolled over after being hit "by extreme winds".
Those killed and hurt are believed to have been working on dousing the Green Valley Fire, around 43 miles (70km) east of the city of Albury.
Thousands of Australians have been told to leave their homes and the surrounding area as wildfires continue to spread throughout the country.
7News's Elspeth Hussey reports from Adelaide where there is little hope that the fires will die down soon
Lightning started 16 fires in Victoria overnight.
Victoria emergency management commissioner Andrew Crisp said fires had generated their own thunderstorms, creating “unpredictable and dangerous” conditions.
He said there had been no confirmed loss of properties in the region.
Victoria emergency services minister Lisa Neville said the worst could be ahead. “This is not yet over.
"We’re really only halfway through what is ahead of us here,” she said.
It comes as highs of 40C (104F) have been recorded in every Australian state, a worrying climate record for the country.
Temperatures on Tuesday were set to hit 33C (91.4F) in Sydney, with hotter weather in the western suburbs.
Thick smoke that has shrouded the city’s iconic landmarks is also expected.
“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,” Rural Fire Services Commissioner Shane Fitzsimmons said.
Event organisers said other activities, including live music performances, could also be cancelled.
“It is a sensible decision for us not to proceed with the fireworks,” the capital territory’s emergency services agency commissioner Georgeina Whelan said.
Total fire bans have been declared in 10 areas, including Sydney, prompting anger over the display.
Critics are calling on authorities to cancel the display and spend the money saved on battling the bushfires, but authorities say the money has already been spent on the fireworks and they do not want to give in to the blazes.
Australian Prime Minister Scott Morrison said earlier that the fireworks should go ahead to show the world Australia’s resiliency.
However, New South Wales deputy premier John Barilaro had said the spectacle should be called off.
“The risk is too high and we must respect our exhausted volunteers,” he wrote on social media before the exemption had been granted.
The western suburb of Parramatta decided to forego a fireworks display.
The popular celebrations are expected to attract one million people to Sydney Harbour’s famous foreshore and generate £69 million for the state’s economy.
An estimated one billion people worldwide watched last year’s display on television.