By Laura Chung and Jenny Noyes
A volunteer firefighter who died when his truck rolled at a NSW-Victoria border town has been named as father-to-be Samuel McPaul.
The fatal truck rollover near Jingellic on Monday night was caused by an "extraordinary weather event" when a "fire tornado" lifted a 10-12 tonne Rural Fire Service truck and flipped it onto its roof, Rural Fire Service Commissioner Shane Fitzsimmons said.
"As it turns out, not only did a truck get blown over, but another command vehicle in the same extraordinary weather event was blown over," Mr Fitzsimmons said.
"To lose one of our own in such extraordinary circumstances is just tragic."
Mr Fitzsimmons said the fire was "indicative of extraordinary fire behaviour we saw overnight and continue to see throughout this morning".
He said Mr McPaul leaves behind "a beautiful wife", Megan, who is pregnant with their first child, due in May.
"As you would expect, the family is grieving and it's been a very difficult night - it would be fair to say I don't even think the comprehension has set in of the enormity of the tragedy and the loss.
"Megan and Sam have been married now for nearly 18 months ... so we've got a completely devastated family, a devastated local community; it has been an extraordinary loss."
Flags at fire stations will be flown at half-mast out of respect, the RFS said on social media.
"Our heart goes out to everyone who knew him, who worked with him and we can't explain or appreciate what his family and loved ones are going through," NSW Premier Gladys Berejiklian said.
A second fire truck passenger, a 39-year-old man, was taken to Melbourne's The Alfred hospital in a serious condition suffering burns, while the driver, 52, was taken to Holbrook Hospital, near Albury, with minor injuries and has since been released.
"It's believed the two passengers were firefighting from the refuge area behind the main cabin when the vehicle rolled," NSW Police said in a statement.
Mr McPaul was involved in the local basketball community. Basketball Wagga Wagga said on Tuesday: "Sam was a well known and admired member of WWBA a few years ago - as our administrator, state league player and coach. He was very well respected by all who played with him or against him and those coached by him." The Illawarra Hawks were planning a minute's silence before their New Year's Eve game against the Sydney Kings on Tuesday.
Unimaginable loss: Morrison
Prime Minister Scott Morrison said Mr McPaul's death was "devastating" and expressed his condolences to his family, friends and brigade members.
"Sam McPaul was a brave firefighter and a member of the Morven Rural Fire Brigade. In one of the cruellest developments, Sam and his wife Megan are due to have their first baby next year. I cannot imagine the terrible sense of loss and grief that Sam's family are now feeling.
"I have spoken to Megan to extend my deepest sympathies and our love and support at this terrible time and express that same sentiment on behalf of the entire country. Sam McPaul was the best of us.
"It is an unimaginable loss and one felt by the entire country.
"This is devastating news and I also extend my sincere condolences to his entire family, friends and fellow brigade members. I thank all of those who are directly involved out there on the fire grounds and the teams supporting them behind the scenes.
"This will continue to be a significant effort in the days and the weeks ahead and I fear, in the months to come. We are expecting more difficult news out of NSW and Victoria today as the assessments are undertaken of the terrible fires from yesterday and last night.
"I am closely monitoring the situation in all states and I am receiving regular daily briefing on all emerging issues. I am also in regular contact with the premiers and fire authorities. To those fighting these fires; please be safe, and continue to pull together in this difficult time. Your country is behind you every step of the way."
NSW Rural Fire Service Association president Brian McDonough said, "Another very sad day as Rural Fire Service volunteers and staff are devastated by the tragic incident which claimed the life of a young firefighter and injured two others yesterday.
"Nothing can take away the pain we all feel when facing such terrible loss."
Third death this month
Mr McPaul is the third firefighter to have died in NSW this month.
Volunteer firefighters Geoff Keaton, 32, and Andrew O'Dwyer, 36, were killed near Buxton, south of Sydney, while trying to contain the Green Wattle Creek blaze on December 19.
After a full day of firefighting , the friends, with decades of firefighting experience between them, were travelling as driver and passenger in a truck convoy near the town when a tree fell on their tanker, which rolled off the road.
Both men, who became fathers within two days of each other in May 2018, were killed at the scene.
Their three fellow firefighters in the tanker escaped the wreck and were taken to Liverpool Hospital.