NSW properties under threat from bushfire

A large fire threatening rural properties in Australia's NSW has been brought under control, but emergency warnings have been issued for two other blazes in the state's central west.

As temperatures climbed relentlessly towards the forecast 40 degree C mark, the Rural Fire Service (RFS) reported 1000 firefighters were battling as many as 100 outbreaks across the state.

An emergency warning has been declared for the central western townships of Rylstone, Kandos and Clandulla with temperatures soaring and ever strengthening wind gusts.

Fire has burnt through 1260 hectares 5km west of the towns and authorities say it is bearing down on them and only about two hours away.

"The fire started on the northern side of Windemere Dam and has crossed the dam," the RFS said.

"It is burning in a southeasterly direction towards Rylstone, Kandos and Clandulla."

Milder conditions overnight allowed firefighters to carve containment lines around the fire.

But with northwesterly winds already gusting up to 75kmh, RFS spokesman Ben Shepherd said: "We're going to have some issues with that in the afternoon.

"As we start to see temperatures top out in the late 30s and those strong northwesterly winds ... that has the potential to throw spot fires in ahead of it."

ABC Radio reported that 19 patients from Rylstone Hospital had been evacuated to nearby Mudgee and Gulgong hospitals before conditions worsened on Sunday afternoon.

Residents have been told to follow their Bush Fire Survival Plan, and if they have any doubts about their ability to protect their property, to leave early.

At 1pm (AEDT) an emergency warning was issued for a fire around the escarpment of Mount Iris, northwest of Glen Davis.

"Under current strong westerly wind conditions, there is a potential for the fire to spot over the escarpment into Glen Davis," the RFS said.

Like Rylestone, Kandos and Clandulla, residents of Glen Davis have been urged to leave properties early if they're not ready to defend them.

But an emergency warning has been lifted for Gunnedah residents in Tara Stock Road where a fire flared on Sunday morning, apparently triggered by fallen powerlines.

At one stage a number of properties were reported to be under threat, but the RFS says the blaze has been brought under control, with the help waterbombing aircraft.

"(The fire) is still burning around some properties but they are getting the upper hand on it," Mr Shepherd said.

"There is still a lot of work to do in quite difficult weather out there."

Meanwhile, thick smoke is expected to cause visibility problems for traffic on the nearby Kamilaroi Highway.

Total fire bans are in place for much of NSW, including the greater Sydney, Illawarra and Hunter regions, with fire danger categorised as severe and extreme for about half of the state.

The Bureau of Meteorology maintains that Sydney's temperature will reach 41 degrees ahead of a cool change late Sunday.

Smoke is blanketing the greater Sydney area, mainly drifting in from fires burning northwest of the city.

"With a hot and dry northwesterly wind blowing, this is sending smoke over the greater Sydney area," RFS Commissioner Shane Fitzsimmons said.

"People with breathing illnesses should be taking precautions such as staying indoors.

"The smoke is expected to remain in the Sydney area until tonight, when a southerly change is forecast."

Health authorities are reminding people to drink plenty of water and stay out of the heat if possible, while the RSPCA has urged pet owners to take extra precautions also.

"Owners need to ensure their pets are kept safe, cool and hydrated to avoid a cruel death," RSPCA chief veterinarian Magdoline Awad said in a statement.

- AAP