The Australian state of New South Wales (NSW) declared its second state of emergency in two months today as temperatures were set to soar above 40 Celsius and nearly 100 bushfires were burning throughout the state, with authorities concerned about fires surrounding Sydney.

The state of emergency will last seven days, running past Christmas, NSW Premier Gladys Berejiklian said.

"The biggest concern over the next few days is the unpredictability, with extreme wind conditions, extremely hot temperatures," Berejiklian told a news conference.

"We have a good sense of where the most concerning areas are, but again, when you have got those turbulent wind conditions, embers and spot fires can occur very unpredictably."

Australia is experiencing a nationwide heatwave. The country recorded its highest average maximum temperature of 40.9 Celsius on Tuesday, and Bureau of Meteorology data shows that record was likely to be exceeded again this week.

- Reuters