Australian officials on Tuesday warned of rising risks of bushfires in the east after about two years of frequent flooding and rain, as a severe heatwave pushed temperatures in several regions, including Sydney, to their highest in two years.

A total of 33 fires are burning across New South Wales (NSW), Australia's most populous state of which Sydney is the capital, with 12 not contained yet. Five public schools have been shut amid a total fire ban across large parts of the state.

Two bushfires have been downgraded from emergency warning levels overnight, but officials said they could flare up again.

"It's going to be another tough day for firefighters and potentially even into tomorrow before we get some reprieve", NSW Rural Fire Service Commissioner Rob Rogers told ABC television. "It's going to take many days to get control on these fires."

No injuries have been reported from the latest bushfires yet but authorities said some residents had to be evacuated.

Many regions in New South Wales on Monday recorded their hottest day since January 2021 with temperatures hitting more than 40 degrees Celsius (104 Fahrenheit).

Temperatures are forecast to reach mid-to-high 30 degrees Celsius on Tuesday but conditions are expected to ease from Thursday. The Bureau of Meteorology said hot and dry conditions along with gusty winds will elevate the fire danger levels.

The state is fighting its worst bushfire conditions since the devastating fires in 2019 and 2020 in Australia's east that killed 33 people, billions of animals and burned an area nearly half the size of Germany.

Since late 2020, Australia's weather has been dominated by La Nina, which brings more rain and floods. But the weather event is "likely near its end" and neutral conditions, which is neither La Nina or its opposite El Nino, were likely to prevail through autumn, the weather bureau said last week.

"People have been really thinking and looking at floods over the last few years, they haven't really been thinking about their fire preparation," NSW Rural Fire Service inspector Ben Shepherd told Sky News.