Australia's military is currently investigating whether a training exercise may have started one of the huge bush fires that is still burning in the state of New South Wales.
he exercise involved explosives and took place the same day the raging wildfire began at a base near the town of Lithgow in the Blue Mountains region.
The wildfires have claimed one life and destroyed at least 100 homes near Sydney. Thousands have been evacuated from their homes, and authorities warned that more homes could be lost as fires burned out of control.
Fuelled by unseasonably high temperatures and strong winds, 100 fires were still burning in New South Wales state in Australia's east, more than 30 of which were uncontained, the NSW Rural Fire Service (RFS) said.
A 63-year-old man died from a heart attack on Thursday while trying to defend his home from a fire in a coastal community a short drive north of Sydney, an RFS spokesman said.
Thousands of people spent the night in evacuation centres on the western outskirts of the city, as well as to the north and the south.
Astonished Sydneysiders watched on Thursday as a thick pall of smoke from the fires in the Blue Mountains west of Sydney moved across the city over some of its best-known landmarks, including the Sydney Opera House and the Harbour Bridge.
Callers to Sydney talkback radio stations on Thursday reported ash and burnt leaves falling on some of the city's famous beaches, including Bondi.
Emergency warnings remained in place for fires in the Blue Mountains and the Central Coast, just north of Sydney.
The biggest threat was on an uncontained fire in Wyong, 75 km (45 miles) north of Sydney, with some homes believed to have been destroyed, the RFS said in its latest update.
NSW Police and Emergency Services Minister Mike Gallacher said the loss of just 100 homes could be considered "lucky" given the magnitude of the threat posed by the fires.
"I suspect given what I saw last night ... I think the potential is most certainly much higher," Gallacher told Australian Broadcasting Corp. (ABC) radio.
Residents said whole streets had been razed in some communities in the Blue Mountains, where schools and businesses were forced to close.
"My son was here, a 19-year-old boy, and we were talking to him on the phone and we simply said grab a few things," Blue Mountains resident Ron Fuller told ABC radio.
"He grabbed his favourite bass (guitar) and a couple of items and he got out, and as he was driving up the street he could see the flames coming into a little gorge behind us and then the next thing the houses were all going up one by one."
Authorities expected to reopen some areas in the Blue Mountains as the weather turned milder on Friday.
With dry weather and a massive land area, Australia is particularly prone to brushfires. In 2009, the "Black Saturday" wildfires in Victoria state killed 173 people and caused $4.4 billion worth of damage.