Police have set up a crime scene as they work to establish the cause of an emergency bushfire which threatened homes on Sydney's upper north shore.
An aircraft initially headed to a fire north of the city was diverted at short notice to help put out the blaze in South Turramurra on Tuesday afternoon.
The Canoon Road bushfire prompted an emergency warning as Sydney faced catastrophic fire danger.
"It is too late to leave," the Rural Fire Service said in a warning message about 4pm.
An aircraft assigned to another fire was quickly diverted to Turramurra to drop fire chemical retardant on the flames.
"We diverted that (plane), turned it around, and got it to rapidly intervene and provide meaningful drop and knockdown effect on that fire in Turramurra," RFS commissioner Shane Fitzsimmons told reporters.
A spokeswoman for NSW Police confirmed a crime scene had been established to investigate the fire.
Officers were seen searching a car and speaking to two young males at Canoon Road.
News footage showed some of the pink retardant had overshot the blaze, coming down on suburban houses and vehicles.
The commissioner was quick to tell residents the retardant would wash off with water.
"Clearly, it's not only hit the mark of the fire, but extended into the road and we've got crews, we've got vehicles, we've got homes, we've got property that is now coloured pink," he said.
"There are guidelines available ... about hosing down and washing down the retardant."
Mr Fitzsimmons said the colour was simply a dye added to the phosphate-based product so aircrews could see where loads had landed.
A nearby fire at Kissing Point Road was briefly at emergency level but was quickly downgraded to "advice" as it was brought under control.
One local said being confronted by fire on their residential street was "overwhelming".
Brad Morgan, 45, said he genuinely feared he might lose the home he has lived in for 15 years, as he described dousing spot fires with water from his pool.
"We could see embers hitting the canopy of the trees - so I put all the valuables and the kids in the car with my wife and sent them away," he told AAP.
"There was no water pressure left in the taps - literally you couldn't get a drop of water - so I ended up getting a bucket from the pool and put out the spot fires we had around."
Student Patrick Kurtesz fled the fire in a stranger's car after stomping on embers in the garden.
The 21-year-old described a "big plume of black smoke" and said he ended up jumping in a car with people passing by.
"Honestly, like I got in the car, and they were such lovely people. But it was really hard for me to focus because I was just like, what if my house has gone down?" he told AAP.
"I keep saying this: it's not supposed to be fire season yet."
A mother-of-three living in nearby West Pymble had packed her bags ready to leave when the fire emergency hit.
The 47-year-old, who did not want to be named, said it felt "very surreal" to be preparing to flee the suburban area she'd lived in for 15 years.
"I never in a million years thought I would be packing, having everything at the door ready to go, waiting to be told 'time to go'," she told AAP.
She said hearing low-flying aircraft overhead had given them "a bit of a fright" and described how she and all her neighbours had been out hosing down the front of their properties on Tuesday in a bid to protect them.