New South Wales fire authorities are bracing for an extremely dangerous day on Wednesday, warning there are no guarantees that more homes and lives won’t be lost.

Crews spent Tuesday trying to contain four major blazes west of Sydney ahead of what is expected to be the worst day by far of the bushfire emergency.

Temperatures are forecast to reach the high 30s, humidity at 10 per cent, and wind gusts of up to 100 kilometres per hour.

Emergency services have closed all schools and childcare centres in the fire zones of the Blue Mountains and some schools in the Southern Highlands and the Hawkesbury.

Hundreds of nursing home residents have been moved to safety.

RFS Commissioner Shane Fitzsimmons says no mass evacuations from the mountains are planned, but if people are unconfident or unprepared they should leave early.

“In leaving early you should do so (Wednesday) morning, well before we start seeing any impact from fire that may advance down through any of these valley systems or out of any of these existing fire lines,” he said.

“The forecast and scenario for (Wednesday) is about as bad as it gets.”

Mr Fitzsimmons says enough people are already in mourning over losses in the latest fire crisis and he does not want to add to it.

“We want to try to do everything to avoid that but I can’t provide a guarantee,” he said.

Earlier on Tuesday, light showers on the state’s major fire fronts lifted the spirits of firefighters conducting aggressive back-burning operations, but they did not slow the advance of the major blazes.

Firefighters deliberately joined the State Mine and Mount Victoria bushfires along the Darling Causeway to help crews manage the situation.

Police on the lookout for arsonists

An 11-year-old boy appeared in court on Tuesday accused of setting fire to an abandoned mattress and lighting grassfire in Newcastle, north of Sydney, last week.

A 15-year-old boy will face court next month over the same fire. Police say the fire caused about 5,000 hectares of damage.

NSW Police Arson Unit Commander Ian McNab says under current conditions, even a small fire can become dangerous.

“It’s just concerning that in these conditions children are lighting fires and these small fires can actually grow very quickly,” he said.

Commander McNab says police profilers have a list of serial arson suspects under surveillance.

“We’ve developed a database of a number of people who have either been convicted or there’s enough intelligence for us to believe that they may be possibly able to light a fire,” he said.

“So we will look at strategies to ensure they don’t light fires on those days.

“Pretty much a proactive approach. If we can prevent a fire it can save a lot of grief.

“One tiny small grassfire on the side of the road can turn into something catastrophic.”

Experts warn city residents unprepared for disasters

Emergency experts say a learned helplessness has left Australians in major cities unprepared to cope in natural disasters.

Lewis Winter from Charles Sturt University told ABC’s Lateline that Australians need to prepare themselves for a situation where emergency services are unable to help them.

“What people have got to know is that they’re on their own, literally on their own,” he said.

“We can’t have a truck or a car at your door when you ring triple-0 in a disaster situation.”

Experts say people should be prepared to look after themselves for at least three days after any major disaster.

But Mr Winter says most people have no plans in place.

“If we turn off power and water, how long will you be able to survive?” he said.