High temperatures mixed with changeable winds will likely spread flames in different directions and pose challenges for tired NSW firefighters.
Doctors have a responsibility to speak out about the dire health impacts of climate change, an expert says, as bushfires burning across NSW create hazardous air pollution in Sydney.
Sydney woke to a thick blanket of smoke as NSW residents are urged to "stay vigilant" amid severe fire dangers and a hot, windy weather forecast.
Parts of the city reached unhealthy levels of air pollution due to smoke from the fires on Tuesday, with areas in north-west Sydney matching the level of air pollution in New Dehli.
Most of NSW's east coast is under severe or very high fire danger ratings as almost 50 blazes burn across the state, with more than half of those uncontained.
A "watch and act" alert was on Tuesday morning issued for an 11,000-hectare blaze at Guyra Road in Ebor, east of Armidale. Activity on the fire's southern edge has increased but the blaze remains under control.
"It's fair to say all of these fires have got the potential to present real challenges today," Rural Fire Service NSW Chief Commissioner Shane Fitzsimmons said on Tuesday.
But Public health physician Dr Kate Charlesworth said the medical profession has an obligation to discuss the link between climate change and poor health.
"From a health perspective, refusing to talk about these bushfires is like refusing to talk about smoking and lung cancer," she told AAP.
"There's a proud history of health professionals standing up on issues of importance - think of asbestos and tobacco control - that is our role."
Dr Charlesworth says doctors are increasingly seeing the health impacts of climate change on patients and speaking up is "part of our duty of care".
The Doctors for the Environment Australia members said poor air quality caused by bushfire smoke puts vulnerable groups at risk, including people with pre-existing heart and lung disease as well as the elderly, babies and young children.
"The key thing is people need to keep their medication at hand - they need to stay indoors, avoid exercise, and see their doctor if they feel it's necessary," Dr Charlesworth said.
The central Sydney air quality rating is poor and people with asthma or other breathing issues are advised to stay indoors, avoid outdoor exercise and seek medical advice as needed. Visibility is also extremely low.
In Sydney's northwest, air quality has been deemed hazardous, with Rouse Hill and Prospect the worst affected areas.
Following weeks of difficult bushfire conditions and last week's 'catastrophic" warnings, Mr Fitzsimmons said it was crucial people didn't take anything for granted.
"The last thing we want is lethargy or complacency or fatigue to set in when it comes to monitoring these conditions," he said.
Six lives and 530 homes have been lost since the NSW bushfire season hit some weeks ago, with more than 420 homes destroyed in the past fortnight alone.
Parts of the state under severe fire danger on Tuesday are Greater Sydney, Greater Hunter, Illawarra-Shoalhaven, Southern Ranges and Central Ranges fire regions.
These regions, along with the Northern Slopes and North Western regions, are also under a total fire ban.
Much of the rest of eastern NSW is under very high fire danger.
Some 1.6 million hectares of land have been lost so far - more than the entire 1993/1994 bushfire season.
Emergency Services Minister David Elliott on Monday said the biggest risk this week would be firefighters becoming fatigued.
A DC10 air tanker has been drafted in from North America to help drop up to 38,000 litres of water and retardant on blazes and efforts will be bolstered by help from New Zealand firefighters, Mr Elliott said.