Air quality in Sydney has plummeted to levels among the world's worst as smoke from bushfires covers the Australian city.
Large areas of the New South Wales capital are on a par with New Delhi in India, one of the world's most crowded capitals.
Although smog is rare in Sydney, better known for its beaches and blue skies, grey clouds hovered over the iconic Opera House and Harbour Bridge, with smoke visible in the air.
The air quality index hit 161 in areas just north of the city centre, reaching a level at which people are advised to avoid prolonged outdoor exercise.
But there could be relief in sight, with the Rural Fire Service (RFS) saying southerly winds should begin to clear the smog.
The smoke had drifted hundreds of kilometres south from fires burning across roughly 136,000 hectares, the RFS said.
Authorities have warned of a high-risk bushfire season in Australia this summer after two quiet seasons, compared with the 2019-2020 "Black Summer" blazes that destroyed a vast area and killed 33 people.
Energy company Santos halted work on a gas project northwest of Sydney as a huge fire raged out of control in the Pilliga forest south of Narrabri, a town that is about 420km away.
"The fires in the Pilliga are of enormous concern," a company spokesperson said in a statement.
"While there is no risk to, or because of, our facilities, we have shut in our operations for the time being."
In New Delhi, where index levels range between 74 and 225, scientists recently planned to turn to cloud seeding to improve matters.
