A bushfire emergency warning, the highest level of alert, has been issued for those living in the New South Wales towns of Rylstone, Kandos and Clandulla about 170 kilometres (105 miles) northwest of Sydney.

The warning come nine months after a firestorm in southeastern Victoria state in which 173 people were killed as fires razed homes and trapped residents in the country's worst natural disaster of modern times.

As temperatures in Sydney reached 40 degrees Celsius (104 Fahrenheit), prompting thousands to flock to Bondi and surrounding beaches, about 1,000 firefighters were battling around 100 blazes across New South Wales state.

Of most concern was the Rylstone/Kandos fire which has burned through some 1,200 hectares (3,000 acres) of bush and has now broken containment lines, despite the efforts of 170 firefighters aided by six helicopters and four planes.

"We've got still a lot of fire activity in that area," Rural Fires Services spokesman Anthony Clark said. "There is still a lot of smoke and the fire is burning in and around properties at the moment."

Clark said one cottage had been destroyed in the blaze while about 40 homes between the small villages of Kandos and Rylstone were under immediate threat.

The emergency warnings for the townships themselves would not be lifted until conditions eased, he added.

"There is still a potential for that fire to affect those communities," Clark told AFP.

The fires come as most of New South Wales has been scorched by a long-running drought and follows a record November heatwave that has swept through South Australia and Victoria days ahead of the southern hemisphere summer.

John Parnaby, incident controller at a fire control centre near Kandos and Rylstone, urged any residents unprepared to deal with fire near their property to leave the area.

"They really should be leaving to find a safer place," he said. "Now would be the right time to go to a neighbouring town."

Rylstone, which acts as a gateway to the World Heritage-listed Wollemi National Park west of Sydney's Blue Mountains, has a population of around 1,200. Rylstone Hospital was evacuated as a precaution.

"People are scared and I think the horrific winds at the moment make people even more on edge," Kandos resident Bonnie Farrell told the ABC.

"I've been a bush girl all my life... this is the first time I've felt threatened as an adult, where I'm the one who had to make the decisions."

Firefighters have another blaze, on the outskirts of Gunnedah in northern New South Wales, under control, officials said.

But in Orange, west of Sydney, an emergency warning has been issued for some residents due to a fast-moving grass fire which is threatening about a dozen properties.

Firefighters are now awaiting a late change in the weather which will bring cooler temperatures to most of the state.