More than 100 fires still burning in Australia

Temperatures in the state's capital Sydney are expected to climb to 35 degrees Celsius on Thursday while the mercury is forecast to soar above 40 degrees Celsius in other parts of New South Wales.

Mount Tomah: An Australian fire official said firefighters battling more than 100 fires across New South Wales would be "challenged with a new threat" when looming heatwave conditions hit the state.

In a news conference on Wednesday, New South Wales Rural Fire Service Commissioner Shane Fitzsimmons said "more than half" of the state's blazes haven't been contained.

Temperatures in the state's capital Sydney are expected to climb to 35 degrees Celsius (95 Fahrenheit) on Thursday while the mercury is forecast to soar above 40 degrees Celsius (104 Fahrenheit) in other parts of New South Wales.

The state's Premier Gladys Berejiklian pleaded for residents 'to be alert' in the lead up to the extreme conditions.

A total fire ban is in place across New South Wales until Sunday.