The heat is rising in New South Wales with one town in the Australian state seeing the mercury jump 15 degrees Celsius in just an hour.

Forecasters say temperatures are rising as Australia braces for a "dome of heat", which is settling in over NSW and Victoria and creating the worst fire risk seen in decades.

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On the NSW south coast, the town of Bega saw a dramatic rise in temperature, recording 37.8 degrees at 9am (11am NZT), according to the Bureau of Meteorology. That was up from 22.9 degrees at 6.30am. Bega has a fire danger rating of severe.

Julie Evans, from the Bureau of Meteorology, said it was a record.''It's never been that hot, that early, in Bega,'' she said.

''The last time it was that hot in the morning in Bega was in  1973, with 36.2 degrees at 9am.''

In Sydney, the mercury is expected to reach 43C  - making it the third highest temperature on record.

Temperatures of 27C were recorded in Sydney at 8am. Broken Hill, the Riverina, and Wagga Wagga all recorded  temperatures over 30C this morning.

The Rural Fire Service has urged people to leave fire-prone areas across the region.

*Follow latest temperatures in Sydney here, see map of fire incidents below.

A fire has broken containment lines in southern NSW and people were urged to take shelter inside as it is too late to leave in safety.

An emergency warning has been issued for residents around Carlaminda in the Cooma-Monaro, with about 10 properties under threat.

We have trucks there and firefighters obviously, we've also got  some water bombing aircraft,'' RFS spokesman Ben Shepherd said.

He said there had been further outbreaks at Bathurst, with a  fire burning near the airport there.

Shepherd also said a fire had broken containment lines near Wagga Wagga.

More than 20 uncontained fires were burning across NSW as thousands of firefighters remain on standby.

RFS commissioner Shane Fitzsimmons said the early high temperatures were not good news for firefighters.

"It's shaping up to be a very difficult day," Fitzsimmons told ABC radio.

"In the catastrophic areas, leaving early is your safest option. It's not about people leaving the big regional centres - we're talking about those that are in bushfire-prone areas.

"Even homes that are well-prepared and well-designed are not designed and expected to withstand the potential fire behaviour and conditions under the forecast.

The state Premier, Barry O'Farrell, has made an emphatic appeal to all residents to be fully prepared for the worst.

A total fire ban has been declared state-wide, and all national parks, state forests and reserves have been closed to the public.

In neighbouring Victoria, a fire has almost doubled in size with firefighters working overnight to stop the blaze hitting   rural communities.

About 500 firefighters and 10 aircraft worked to battle the Kentbruck blaze in the state's southwest which had burnt out 7050 hectares last night.

The Country Fire Authority was closely monitoring northern parts of the state where a severe fire danger rating had been issued.

KIWI HELP

Australian fire authorities have called for rural fire fighting support from New Zealand with two crews expected to leave tomorrow.

National rural fire officer Murray Dudfield said they would be deployed to Tasmania, but he expected the request to be extended to NSW.

He received a call for assistance late last night.

''The Tasmanian fire agencies together with the Department of Parks and Wildlife and the Tasmanian Forestry Commission have requested that we provide two remote firefighter crews which we will be agreeing too,'' Dudfield said.

Dudfield said the crews would come from areas such as Northland, where there had been a higher rainfall recently.

"In those places that have had a lot of rain, there would be no problem with pulling resources from there for a 16-day period."

Residents on a southern Tasmanian peninsula have been urged to seek refuge ahead of a renewed bushfire threat across the region.

The Forcett bushfire has destroyed more than 100 homes since last week, concentrated in the town of Dunalley.

The region has largely been isolated by road since last week but volunteers, charities and emergency services have been bringing supplies in - and evacuating people - by boat and ferry.

Tasmanian Fire Service senior station officer Phil Douglas said around 40 bushfires were burning with concerns also held for out-of-control bushfires at Lake Repulse, north of Hobart.

He said strong wind gusts between 30 and 70kmh were expected to sweep across early this afternoon causing concern for communities north of any active fires.

He said authorities were ready for possible evacuations.

MORE SCORCHERS AHEAD

Australia Prime Minister Julia Gillard toured the fire ravaged state yesterday and warned people to expect more danger.

Gillard said extreme bushfires were part of life in a hot and dry country.

''And while you would not put any one event down to climate change ... we do know that over time as a result of climate change we are going to see more extreme weather events,'' she said.

Walking through the remains of the Dunalley primary school in Tasmania yesterday, she said people in NSW needed to be prepared.

''Everyone can remember what their school was like, how they saw their kids grow. This is a devastating scene,'' she said of the twisted roofing iron and scorched earth.

''But the worst thing is if human lives are lost.''

Map of current incidents from the NSW Rural Fire Service:

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