Thick smoke from bushfires is likely to blanket Sydney for at least another day as almost 50 blazes continue to burn across NSW, two of which have now been upgraded to "emergency warnings" as conditions deteriorate.
The Myall Creek Road bushfire in northern NSW was elevated to an emergency warning on Tuesday afternoon after it came within a couple of kilometres of Whiporie, threatening the village.
"(The fire) is moving fast through pine plantation. If you're in the Whiporie area seek shelter ... it is too late to leave," The Rural Fire Service tweeted.
The 144,000-hectare bushfire at Gospers Mountain was also upgraded to an emergency warning just before 8pm after it picked up "dramatically" and began to "flare and run".
People living in the Colo Heights area have been advised to see shelter as the fire approaches.
One other NSW fire has been classed as "watch and act".
The Gospers Mountain fire has sent smoke over Sydney, and the Bureau of Meteorology says the haze is likely to be repeated on Wednesday.
The smoke could clear overnight but "the conditions are really there for that sort of thing to return", the bureau's NSW regional manager Ann Farrell told reporters.
"We really aren't going to be out of the woods for the coming days with that air quality issue from smoke over the eastern part of the state."
Air quality was hazardous on Tuesday afternoon in Sydney's east and northwest, as well as on the Central Coast, the Northern Tablelands and northwest slopes.
People with asthma or other breathing issues were advised to stay indoors, avoid outdoor exercise and seek medical advice as needed.
NSW Health director Dr Richard Broom said Sydney's air quality "would at the very least be comparable to some cities in developing countries where they have very poor air quality".
"On days when there's high air pollution we see increased rates of hospital presentations and increased numbers of deaths as well, so it's undoubtedly serious," Dr Broom told reporters, adding people with pre-existing conditions should be cautious.
Dust is also affecting air quality and a wind change expected on Thursday could exacerbate the problem from the state's west through to the coast, Ms Farrell said.
That change could trigger thunderstorms into the weekend which won't bring much rain but could see lightning strikes ignite additional fires.
Parts of NSW could experience heatwave conditions this week with the state's west forecast to reach 40C and western Sydney expected to hit the high-30s.
A state of emergency declared by Premier Gladys Berejiklian ended on Tuesday, but NSW Police deputy commissioner Gary Warboys says emergency services could reach out to her again.
"It's been pretty clear that if we need (a state of emergency) government is in a position to, and keen to, assist us to provide protection and safety to the community," Mr Warboys said.
The Rural Fire Service on Tuesday said 577 homes had been destroyed to date this fire season, with more than 420 lost in the past fortnight. There have been six deaths.
Additional "watch and act" alerts were in place on Tuesday afternoon for a 15,000ha blaze at Ebor, east of Armidale, and a 21,000ha fire at Bora Ridge, west of Evans Head.
Some 1.6 million hectares of NSW bushland have been lost so far this bushfire season.
Australian Associated Press