Ash has been falling in the backyard of Kazan Brown’s home on the eastern edge of the Blue Mountains for three weeks. A heavy veil of smoke has turned the sun red and blocked out the stars. The smoke is scratching her throat and burning her eyes. The sheets smell like smoke. Clothes smell like smoke.

“You wake up in the morning and you can smell the bush burning,” Brown says. “It’s eerie, the feeling around town. Everyone is nervous … the panic is catching. It’s spreading just like the fire.”

The Blue Mountains separate Sydney from the plains. A 162,000 hectare blaze known as the Green Wattle Creek fire has been burning uncontrolled towards Warragamba, the village on the edge of Sydney’s largest water reservoir. Brown is Gundungurra, a traditional owner of the area; her family has been living here for 50,000 years. The fire has already burned through world heritage rock art sites, made charcoal out of scarred trees and destroyed her family property of Gungarlook.

“We will not be leaving,” Brown says.

They have been sticking close to home for a fortnight, worried that if the wind changes they will be stuck on the wrong side of a roadblock. When Warragamba last burned, on Christmas Day 2001, 30 homes were destroyed and the bridge across the Nepean River closed for weeks, cutting off access. The Browns defended their homes then. Now Christmas is upon them again and Brown has cancelled plans to host and told her relatives to stay away.

Brown lives in a fibro workers cottage built in the 1940s. Her sister and 70-year-old mother live in similar houses. They’re flammable, often contain asbestos, and do not have a thermal mass, like a concrete block wall, to shelter behind if the fire burns over.

Brown lives two streets away from the forest but her mother and sister are separated from the trees by a 50m “firebreak” of long, dry, grass. The land is owned by WaterNSW but they haven’t mowed it in years.

“Their backyard is the bush,” Brown says. “If anything happens down there they can come up here, and if it gets here we can go to the evacuation point in town.”

Throughout Australia, thousands of people are making the same calculation. There are more than 100 fires burning in New South Wales, and dozens more in Queensland, Victoria, and South Australia. Christmas plans are supplanted by bushfire survival plans.

“Your safest option is to leave,” NSW deputy fire commissioner Rob Rogers said on Friday. “We cannot guarantee that we will be able to get warnings out to everybody … so don’t sit there waiting for a text message.”

The risk is not limited to those living in a fire zone. The Saturday before Christmas is a traditional day to get out of the city, but for those leaving Sydney it meant driving through catastrophic bushfire conditions.

That’s the top of Australia’s bushfire danger rating index and denotes unsurvivable, firestorm-type conditions. South Australia had catastrophic conditions on Friday, on the heels of Australia experiencing its three hottest days ever recorded.

The message from authorities before Saturday was that a failure to change travel plans – to change Christmas plans entirely, if necessary, to avoid bushfire prone regions – would be selfish. But Sydney has been choked by smoke for weeks. People are desperate to leave.

Smoke from bushfires rises into the air near Sydney, New South Wales. Photograph: Dean Lewins/EPA

As of Friday, 800 homes have been lost to bushfire in NSW, 40 in Queensland and an unconfirmed number in South Australia. Six people died in fires in November. Two volunteer firefighters were killed when their truck rolled near Buxton on Thursday and three more are in an induced coma after their truck was engulfed in flames at an earlier incident at the same fire, the Green Wattle Creek blaze.

That fire also burned through Balmoral on Thursday, leaving the village surrounded by flames and destroying up to eight homes. The fire station sounded its emergency alarm five times, a call for residents to run from their homes and shelter in the station until the immediate threat has passed.

“A massive amount of village was taken yesterday … and then the lives and the injuries,” says Brendan O’Conner, the captain of the local fire brigade. He is visibly shaken talking to Guardian Australia on Friday. “It’s just such a tragic thing, unfortunately we’ve seen too much of it this year. It’s just wearing everyone down.”

A short distance east of Balmoral, a couple is nervously watching the ridgeline for the moment when the flames roar over the top. They have lived on this bush block for 20 years and say they “always defend”. They managed to save their property in the 2013 fires, and have had their defences checked by the local fire captain.

“It’s going to be bad,” the man, J, says. “If the wind picks up everyone is going to be in trouble. Heat we can manage but wind is what drives the fire. With that southerly that came through [on Thursday], you saw what happened to Bargo.”

Further north in the Blue Mountains, the mayor, Mark Greenhill, is nervously watching a fire that has entered the Grose Valley. Under a strong northerly wind, it will run through the lower Blue Mountains.

Greenhill talks in short bursts, interrupted by emergency warnings. The council offices are in Katoomba, hemmed on three sides by uncontrolled bushfires: the 450,000ha Gospers Mountain “megafire” to the north and east and the Green Wattle Creek and Megalong Valley fires to the south.

“Fire on three sides is unprecedented,” Greenhill says.

The Blue Mountains have burned many times. In 2013 they lost 203 homes. In the past week they have lost 11 more.

The forest is “incredibly, unprecedentedly dry”, Greenhill says. The soil is a dry powder.

“There has been a profound lack of rain,” he says. “I drive through [the mountains] now and the trees are just brown.”

The sky is no longer an unending blue.

“What I have now is a sky that is close to me and is brown,” Greenhill says. “You sometimes wonder if it’s ever going to be the same again.”

Ian Woolley is a volunteer firefighter with the Kulnura brigade on the Central Coast of NSW. Two weeks ago he and his colleagues were defending their town from an emergency level fire which later that night joined the Gospers Mountain megafire. Some neighbours lost buildings when winds changed and sent the fire through town from different directions.

“My wife, this was the first major fire she’s faced, she was home by herself and was scared,” he says. “There’s still fire burning in the gully from my place. There will still be trees smoking, dead trees burning on the inside.”

Trees like that are called “widow-makers” by older firefighters because they drop without warning. When the roar of the flames has passed you can hear them creaking in the wind.

It has been “a lot of long days”, Woolley says. He and the rest of his volunteer brigade have been doing full-time firefighting for weeks. His regular employer is continuing to pay him but other members aren’t so lucky. They are either going without pay, have had to stop defending their community, or are trying to do both and running on empty.

They have sufficient resources to cover the fires at the moment, Woolley says, but not if the fire season is this bad every year.

“If it does become the new normal there needs to be more resourcing,” he says.