Loading "Three other passengers were injured and were treated at the scene by NSW Ambulance paramedics. "A crime scene has been established and the Crash Investigation Unit will investigate the circumstances surrounding the incident." The RFS described it as "an absolutely devastating event in what has already been an incredibly difficult day and fire season". The fire truck was believed to have been travelling in a convoy during firefighting operations when the fatal crash occurred, the RFS said.

"The service’s thoughts are with all the firefighters' family, friends and fellow brigade members," it said. Loading Replay Replay video Play video Play video Firefighters injured in separate incident Thursday was among the most trying days of the fire season, which has so far destroyed almost three million hectares of land in 105 days. Loading

In the areas of Bargo, Balmoral and Buxton at least 20 structures were lost on Thursday, including at least 12 homes. Earlier in the day, three other firefighters suffered burns in the Green Wattle Creek Fire when their crew of five firefighters was overrun by flames near Bargo, south-west of Sydney. Two male firefighters, aged 36 and 56, were flown to hospital where they were intubated after suffering burns to their faces, airways and bodies. A third person, a 28-year-old woman from the same crew, was taken by road ambulance to hospital suffering minor burns and smoke inhalation. "This particular crew, a crew of five, were overrun by fire. Enveloped by fire," RFS Commissioner Shane Fitzsimmons said.

"You've got this relentless onset of hot, dry, windy conditions and, until we see a meaningful reprieve in weather … the reality is they're [the fires are] not going out. "We're up around 8500 fires so far this season. So that's the sort of challenge that firefighters and emergency services personnel are facing every day, and we've seen it day in, day out, week in, week out, month in, month out now since winter." At the peak of Thursday's bushfire emergency, four fires were burning at emergency warning level, while soaring 40-plus degree temperatures and choking smoke covered greater Sydney on what was the hottest day of the summer so far. The four emergency warning level fires stretched from the Hawkesbury to the Shoalhaven. Among the most volatile was the Green Wattle Creek fire, which is more than 167,000 hectares in size and is burning 15km south-west of Warragamba Dam Wall in the Blue Mountains National Park. Loading

On Friday morning, the Green Wattle Creek fire was the only blaze that continued to burn at emergency level. A strong southerly change with gusty winds hit the Green Wattle Creek fireground overnight, pushing the fire in a northerly direction towards Thirlmere, Tahmoor and Nattai. "Dangerous fire conditions and erratic fire behaviour are being experienced across the fireground," the RFS said, adding that properties "are currently under threat".

State of emergency declared Loading NSW Premier Gladys Berejiklian on Thursday declared a seven-day state of emergency, with weather conditions this weekend shaping up to be even more problematic for firefighters. Under the state of emergency, Commissioner Fitzsimmons has extraordinary powers including the ability to evacuate properties, close roads, pull down infrastructure at risk of collapse and order the shutdown of essential utilities such as electricity, gas, oil and water. While fire conditions are expected to worsen by Saturday, conditions are expected to ease on Friday.