People in Sydney woke up to a city shrouded in smoke on Tuesday, as scores of bushfires rage across the region.
Strong winds overnight brought smoke from fires inland, pushing the air quality in Australia's largest city to beyond "hazardous" levels at times.
On social media, locals have described hazy skies and the stench of smoke in their homes.
About five million people live in the state capital of New South Wales, which has been affected for weeks by fires.
Six people have died in bushfires in the state's north since October.
Sydney residents were warned about severe fire danger on Tuesday, as temperatures soared to 37C (98.6F) in the city's west.
Parts of the city recorded air pollution levels at eight times higher than the national benchmark.
Health officials advised people to stay indoors and avoid physical activity. They also shared first aid guides on how to help asthma sufferers and others with respiratory problems.
"The smoke is likely to hang around for the next few days," warned the New South Wales Rural Fire Service.
'Coughing and spluttering'
Frances Mao, BBC News, Sydney
You could smell it the moment you woke up. At first I hoped that it was just my housemates smoking inside again - but I knew deep down it was another fire. The sky was a burnt grey.
The first thing I checked on my phone wasn't Instagram, or emails, but the app I downloaded last week which shows where the bushfires are.
Thankfully, no new fronts had sprung up overnight. But it's hard to predict these days - the blazes are so volatile and can flare up with a change in wind.
I cut short my walk to work to get the bus instead. People were still coughing and spluttering on board. I made a mental note to buy a face mask - something I've never needed before in Sydney.
Last week, Sydney faced unprecedented bushfire danger when blazes hit its suburbs and parts of its outskirts.
Authorities said the source of the smoke on Tuesday came from a blaze in Wollemi National Park, 150km (93 miles) north-west of the city, which had grown to 150,000 hectares in size.
What's happening with the fires now?
Close to 50 bushfires continue to burn in populated coastal and inland regions to the city's north. Authorities say 468 homes have been destroyed since blazes flared up on 8 November.
Four people were confirmed to have died in the fires since then: Vivian Chaplain, 69, Julie Fletcher, 63, Barry Parsons, 58, and George Nole, whose age is unknown. They were found in separate locations in rural NSW.
A couple, Bob Lindsey, 77, and Gwen Hyde, 68, were killed in a bushfire in the same regions in October.
Many of the affected areas have experienced thick smoke and extremely poor air quality for weeks.
Officials have warned that blazes could escalate later this week when heatwave conditions reach New South Wales and neighbouring Queensland, where scores of fires are burning.
Meanwhile, a "catastrophic" fire danger warning has been issued for parts of South Australia. The state capital, Adelaide, is forecast to reach 42C on Wednesday.