There are fears a suspicious bushfire that destroyed a Blue Mountains home and damaged many more could flare up and start heading towards houses on Sunday if strong winds persist.

Amid the dangerous fire conditions on Saturday, fuelled by gusty winds and the hottest temperature recorded in Sydney since January, more than 1000 firefighters were deployed across the state to wrestle with more than 70 fires.

The worst fire, at Katoomba, suspected of being deliberately lit, heralded an unnerving start to the fire season for the community that lost more than 200 homes little more than a year ago.

Rural Fire Service Commissioner Shane Fitzsimmons said many experienced firefighters described the conditions and fire behaviour as the worst they had seen in more than 40 years.

He said strong winds were expected to fan the flames overnight and the fire would not be contained on Sunday.

"This fire will be requiring work now for days," he said. "It's burning in some very difficult country."

Blue Mountains mayor Mark Greenhill praised the resilience of his "tough community".

"We've been here before," he said. "We have a habit of seeing these things through."

The blaze, which had been contained throughout the day, became unmanageable in the afternoon as wind gusts of up to 90km/h swept over the mountains.

Residents were advised not to evacuate for fear of blocking the narrow roads and impeding the access of fire trucks.

One firefighter was taken away and received hospital treatment for smoke inhalation.

A resident was also taken to hospital to be treated for chest pains.

One fire truck was engulfed in flames but the vehicle was not damaged and no one was injured.

A 15-year-old boy died after he was struck by lightning at a beach in Port Stephens.

The boy had been surfing with friends and an adult at One Mile Beach, near Anna Bay, when an electrical storm blew over about 5.10pm.

In Port Stephens there was also a large bushfire in coastal heaths but it was not causing any immediate threat.

Lisa Kearney, who lives with her 12-year-old daughter and twin 19-year-old sons in the Blue Mountains, said she grabbed the cat, birth certificates, some photos and clothes when embers began falling around her house.

"I could see the flames on that house [that was destroyed] as it was going," she said. "It was eerie. It came over so dark and eerie."

As night fell, the fire was downgraded to "watch and act" status after 200 firefighters assembled in the area with five helicopters, ready to continue water-bombing the fire at first light.

RFS Deputy Commissioner Rob Rogers told Fairfax Media that there was a suggestion the fire had more than one ignition point, which led to the belief it may have been suspicious.

"There is no apparent natural cause and there was no report of a lightning strike or anyone saying they had an accident with a fire or anything like that," he said.

The RFS said there were 72 bush or grass fires across the state with 37 uncontained and more than 1000 firefighters in the field.

"Well above average" temperatures and thunderstorms marked the start of November, with Observatory Hill in Sydney reaching 36.5 degrees and Sydney Airport the hottest place in the city at 37 degrees - 13 degrees hotter than the average for this time of year.

The State Emergency Service said gusts in the south Penrith area of 75km/h brought an increase in calls with trees down and loose items flung around.

The service answered about 80 calls in western Sydney in an hour but there were no reports of injuries.

The Blue Mountains tourism board had only just launched an initiative to encourage visitors back to the area when the bushfire struck.

High fuel loads, coupled with warm, dry and windy weather, provided the dangerous conditions that fuelled last October's fires.

Blue Mountains tourism boss Daniel Myles said the visitor attractions in the area were not threatened.

He quoted Aunty Sharyn Halls Gundungurra, an elder who spoke on the anniversary of last years' fires two weeks ago: "Whether there are fires or whether there are storms the Blue Mountains is open for business."