The Bureau of Meteorology on Tuesday evening warned things will get worse before getting better.
More than 70 fires are burning from near Nowra all the way up to the Queensland border with bureau state manager Ann Farrell saying the situation is changing "very rapidly".
"We're looking at a wind change that's really going to worsen things dramatically through the night," Ms Farrell said.
A low-pressure system moving across the state is bringing "strengthening" winds that will increase fire danger on Tuesday evening.
"It won't be until tomorrow morning that we see it clear the northeast of the state," Ms Farrell said.
"Things are going to be pretty difficult for some time tonight before we see any real improvement in firefighting conditions."
NSW Rural Fire Service Commissioner Shane Fitzsimmons said firefighters and affected communities were facing "a really long night".
He said there would sadly be no rainfall in the southerly change and warm, dry conditions are set to dominate in the days and weeks ahead.
"As we look out a little bit further, we're expecting a cyclical pattern of increasing temperatures as we head into the end of this week and indeed as we head into next week," he said.
Premier Gladys Berejiklian in parliament on Tuesday said the state was expecting "the worst fire season imaginable".
"It's barely the end of spring and we've already witnessed that already," she said.
"Extreme weather conditions due to the deep drought are likely to continue over the next few months and beyond."
Police investigate Sydney blaze
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 Rd bushfire prompted an emergency warning as Sydney faced catastrophic fire danger.
"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 Fitzsimmons said.
NSW Police Force confirmed an investigation is underway.
Officers were seen searching a car and speaking to two young males at Canoon Rd.
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 Rd 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".
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."
Source: NSW Rural Fire Service
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.
'My house is burning down, what are you doing?'
Labor leader Anthony Albanese spent the day meeting with residents in the Northern Rivers community of Nimbin.
However, the public appearance turned sour as Labor MP Janelle Saffin was confronted by a resident demanding more action to help the community.
"Shame on you. Your house is not burning. My house is burning down! What are you doing? Nothing! You're laughing. You're having a circus. You're playing with fire," Ginger O'Brien said.
"Get more money for [the firefighters]. When did you send aid? When have you given them more money? You've taken it all away."
The prime minister and his government have also proven unpopular in the streets of Nimbin, with some locals turning out with signs to vent their frustration with Canberra.
Authorities are warning NSW residents not to underestimate the damaging effects of smoke as air quality worsens amid the state's bushfire crisis.
The latest air quality index rating has recorded 221 micrograms of particulates per cubic metre in Sydney's east, while the lower Hunter's figure of 306 was the worst in the state.
Dust has also contributed to poor air quality in Sydney, Newcastle and the Central Coast ahead of a southern change expected to hit on Tuesday evening, the Bureau of Meteorology said.
NSW Ambulance Commissioner Dominic Morgan said the smoke was causing "slightly above-average demand" on services, with almost 100 asthma or breathing-related calls since Tuesday morning.
Of those, 39 were from the Sydney area and another 35 were from the north of the state where the majority of fires are burning.
In one case paramedics treated a patient who no longer had their reliever medication.
Mr Morgan urged asthmatics and others vulnerable to respiratory issues to remain vigilant, or the consequences could be fatal.
"To fail to make a plan when you have an asthma condition or respiratory condition and not have reliever medication, this could be a deadly condition for you," he said.
"So make a plan and get medical aid as soon as possible."
Four 'caught breaching NSW fire ban'
Three men have allegedly breached NSW's total fire ban while a nine-year-old boy has admitted to lighting a fire with a blowtorch as blazes rage throughout the state, according to NSW Police Force.
Police allege the first incident saw a 27-year-old man light a small campfire at Wallacia in Sydney's west on Monday afternoon to boil water for cups of tea.
He immediately extinguished the flames when police and firefighters arrived and was issued an on-the-spot $2,200 infringement notice.
Hours later, police were called to a home at Prestons in Sydney's south-west, where a 35-year-old man allegedly burned fence palings in a cylindrical barbecue.
"Embers from this fire fell to the ground and ignited palings, causing a secondary blaze," NSW police said in a statement.
Both fires were extinguished and the man was also issued an infringement notice.
The third man will face court after he allegedly lit a small coal barbecue at a Lalor Park home in Sydney's west in the early hours of Tuesday morning.
Fire and Rescue NSW extinguished the fire and the 46-year-old man was arrested for failing to comply with a total fire ban and breach of bail.
The nine-year-old, due to his age, was warned under the Young Offenders Act after a small grass fire broke out behind a street in Nowra on the South Coast about 11.35am on Tuesday.
Police say the boy, who was with a group of other children, admitted to lighting the fire with a blowtorch.
The total state-wide fire ban remains in place and has been extended into Wednesday.
It means people cannot light, maintain or use a fire in the open, or carry out any activity in the open that causes, or is likely to cause
Army on standby
Ms Berejiklian on Tuesday morning said the dire forecast had not changed and told residents to heed the warnings of authorities and head for safety.
"We need to make sure every community member takes the opportunity to assess the situation and act with precaution in every possible manner," Ms Berejiklian told reporters in Sydney.
"I can't thank enough volunteers and personnel that have been on the ground."
Defence Minister Linda Reynolds has said ADF personnel were not trained firefighters but they would be on standby to provide other support if needed.
Hundreds of schools have been closed for the day, with Education Minister Sarah Mitchell saying "safety remains the number one priority".
Emergency Services Minister David Elliott said residents face what "could be the most dangerous bushfire week this nation has ever seen".
Mr Elliott said places, where fires are already raging and are not contained such as the mid-north coast and north coast, are "going to cause us problems".
But he added the mission is to "overwhelm" any new fires elsewhere with fire trucks and aircraft so they don't take hold.
There are extreme fire danger ratings - the second highest - in place for the North Coast, Southern Ranges, Central Ranges, New England, Northern Slopes and North Western areas.
Fires since Friday have claimed the lives of three people and destroyed at least 150 homes.
More than 100 people have been injured including 20 firefighters hurt trying to protect communities.
NSW Ambulance Commissioner Dominic Morgan is considering bringing in extra resources from interstate to cope with the demand.
Climate change dispute
Recent days have seen a war of words break out over a potential link between the fires and climate change.
Climate protesters have gathered outside Nationals leader Michael McCormack's office on Tuesday after he condemned the "disgraceful, disgusting" behaviour of "raving inner-city lunatics" linking climate change to the blazes.
Ms Berejiklian said on Monday that now is not the time to discuss the issue, but insisted her government has not shied away from talking about it and will discuss it at another time.
But some of those living in rural regions who have been directly affected made their feelings clear.
"To disregard the issue of climate change in a situation like this is wrong," Cerene Lowe, whose home was among many razed in Wytaliba on Friday told AAP.
Fellow Wytabila resident and Glen Innes Severn mayor Carol Sparks, whose home was severely damaged in a blaze, said there was "no doubt" about the link to climate change.