NSW fire crews brace for extreme heat and wind

Firefighters in New South Wales are bracing for extreme conditions on Wednesday, with hot, dry temperatures and strong winds forecast.

Light showers on the Australian state's major fire fronts lifted the spirits of firefighters conducting aggressive backburning operations on Tuesday, but have not slowed the advance of the blazes.

Crews were racing to get some control over several fires, amid warnings that the weather on Wednesday may be more dangerous than first thought, the ABC reports.

The Rural Fire Service says conditions across fire-hit areas of the Blue Mountains, west of Sydney, are forecast to be "about as bad as it gets". Temperatures are predicted to be in the high 30s, humidity at 10% and wind gusts at up to 100kmh.

Rural Fire Service Commissioner Shane Fitzsimmons says there is a very real potential for more loss of homes and loss of life.

All schools in the Blue Mountains and some in the Southern Highlands will be closed and Blue Mountains residents are being urged to evacuate by lunchtime.

Hundreds of firefighting reinforcements have headed to New South Wales from other states.

More than 1000 firefighters and 200 fire engines will be operating in the Blue Mountains on Wednesday. Ninety aircraft assisted the battle to control three fires on Tuesday, with a similar number expected to be in the air on Wednesday.

The state's fire and rescue commissioner, Greg Mullins, said it is the biggest turnout in the state's history.

Two bushfires merged

Bushfires at Lithgow and Mt Victoria in the Blue Mountains were merged on Tuesday "in a controlled way" along the Darling Causeway, a Rural Fire Service spokesperson said.

It was a bold strategy to try to stop them joining with a third, uncontained fire at Springwood, ahead of the forecast strong winds. About 2000 firefighters were being rotated through frontlines in the Blue Mountains.

There has been large-scale backburning taking place around the four major bushfires. An emergency warning for the State Mine fire at Lithgow was downgraded to watch and alert; the same status as Mt Victoria and Springwood, and in the Southern Highlands.

Second boy charged

A 15-year-old boy has been charged over a bushfire that destroyed more than 5000 hectares in the Hunter region last week.

The boy was charged at Raymond Terrace police station on Monday evening with intentionally causing fire and being reckless as to its spread, AAP reports.

He is the second youth to be charged in relation to the fire in the Heatherbrae area in Port Stephens. An 11-year-old boy was charged over the fire on Monday.

Three other children have been arrested and accused of lighting the blazes that ripped through parts of New South Wales last week.

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