Sydney:Australian authorities on Monday issued fresh warnings about a "mega blaze" after it spread beyond containment lines and razed 20 houses near Sydney.
The mega blaze, also known as the Gospers Mountain fire, burning over about 400,000 hectares, has moved further into the Blue Mountains a popular tourist area that lies west of the city.
Firefighters had tried to use cooler temperatures for "back-burning" a tactic of deliberately starting small fires to remove vegetation before dangerous conditions arrive.
But the tactic backfired and crews lost control of the back-burn, said NSW Rural Fire Service deputy commissioner Rob Rogers.
About 20 homes were destroyed as a result amid 229-ft flames, he added.
Read more:Uncontained fires rage through New South Wales
Meanwhile, a heatwave forecast for later this week could bring the nation's hottest day on record.
Temperatures could exceed the 50.7 degrees Celsius record set in Oodnadatta, South Australia, in 1960, according to the Bureau of Meteorology.
Since September, six people have died in a bushfire crisis that has engulfed the eastern states of New South Wales (NSW) and Queensland.
The blazes have destroyed more than 700 homes and blanketed towns and cities in smoke.
Last week, parts of Sydney suffered air quality 22 times worse than the clean air standard. Australia's largest city has about five million residents.
Also read:Sydney choked by hazardous haze from Australia bush fires
