More than 3,000 firefighters in Australia are battling devastating bushfires raging across New South Wales as weather conditions worsen.

"This will be as bad as it gets," Rural Fire Service chief Shane Fitzsimmons said, adding there was "real potential for more loss of homes and life".

High temperatures, low humidity and strong winds of up to 100km/h (60mph) are forecast for Wednesday.

In total, 59 fires are burning across the state, 19 of which are uncontained.

Hundreds more firefighters have been deployed to the Blue Mountains, to the west of Sydney, to work alongside the 1,000 already there, making it one of the largest firefighting contingents ever assembled in the state's history.

Residents have been urged to leave affected areas. Hundreds of nursing home residents were evacuated late on Tuesday and all schools in the area are closed.

"We are all in this together and we are going to get through this day. If you haven't prepared yourself, for those in the Blue Mountains, now is the time to leave," NSW Premier Barry O'Farrell said at a news conference on Wednesday morning.

"We hope, of course, today's conditions and potential events do not occur. We've planned for the worst but we continue to hope for the best."

Up to 5mm (0.2in) of rain fell across fire grounds on Tuesday night and into Wednesday morning.

"Whilst that is some welcome relief in terms of moderating the current fire behaviour, it has compromised considerably the ability to continue with the back-burning operations that were planned throughout the evening," Mr Fitzsimmons said.

Back-burning is controlled burning of key areas aimed at depriving a fire of fuel and prevent it travelling in a certain direction.

In the Blue Mountains, there are four "watch-and-act" alerts in place for the State Mine fire near Lithgow, the Mount Victoria fire, the Hall Road fire near Wollondilly and the Linksview Road fire near Springwood, according to the NSW Rural Fire Service.

On Tuesday fire crews deliberately joined two large fires - State Mine and Mount Victoria - in order to prevent them linking up with a third to create a massive blaze.

The fires have been burning in the Blue Mountains since Thursday, with a state of emergency declared at the weekend.

"There's not been fires quite like this before - so big, so intense and so fast. We're talking about a fire that at some points is five storeys high," Mayor of the Blue Mountains Mark Greenhill told the BBC on Tuesday.

"[Wednesday] is going to be a horror day in terms of the weather and could be a horror day in terms of the fire," he said.

Police and Emergency Services Minister Michael Gallacher said residents in the Blue Mountains needed to have a plan.

"Pack the car now, head down the mountain, come down and enjoy time in the metropolitan area and allow the firefighters the freedom to move through the community to protect your homes," he said.

Sam Buckingham-Jones, who is from Springwood, said he was ready to evacuate if necessary.

"There has been a very strong wind today, about 100km/hr," he told the BBC.

Minister Michael Gallacher: "Things are heating up"

"There is a bushfire only 100m away from where we live. Everyone here is talking about what would they take with them if they have to evacuate - we packed a lot of stuff in the cars and we are ready to leave if we have to."

Further north, an "emergency" alert has been issued for a fire on the outskirts of Newcastle, with residents in Minmi told to leave.

So far the fires in New South Wales have destroyed more than 200 homes. One man has died, possibly of a heart attack while defending his home.

New Prime Minister Tony Abbott, meanwhile, has hit back at comments by UN climate chief Christiana Figueres linking bushfires to global warming and criticising his decision to repeal a tax on carbon emissions introduced by the previous government.

"The official in question is talking through her hat," Mr Abbott told local media.

"Climate change is real, as I've often said, and we should take strong action against it. But these fires are certainly not a function of climate change - they're just a function of life in Australia."

Mr Abbott, who took office in September, has drafted legislation to repeal the carbon tax, which imposed a levy on the country's 300 biggest polluters.

The new prime minister, who says the tax cost jobs and forced energy prices up, wants to introduce a Direct Action plan under which farmers and industry will be paid to act to reduce emissions.