Authorities warn of hazardous air quality with higher concentrations of particles per million than cities like Jakarta.

Sydney residents coughed and spluttered their way around Australia‘s largest metropolis on Thursday, as a bank of smoke from rural bushfires enveloped the city, prompting health warnings.

Smoke from out-of-control fires to the north of the city prompted health authorities to warn residents with respiratory problems to avoid outdoor physical activity.

“If you really want to keep out of the smoke, the best thing you can do is stay indoors, keep your doors and windows shut,” said Richard Broome of the New South Wales’ Ministry of Health.

Firefighters are struggling to contain dozens of blazes, including one caused by a lightning strike far north of the city that has ravaged an area of over 2,000 hectares (4,942 acres).

Strong winds have pushed the fumes towards Sydney, shrouding landmark buildings such as the Opera House and Harbour Bridge where the air has taken on an acrid taste.

“The smoke will likely persist for several days and may not clear until some stage over the weekend,” said New South Wales Rural Fire Service said on Thursday.

In contrast to many of Asia’s major cities, Sydney’s residents and visitors usually have clear skies and clean breezes.

Authorities on Thursday rated the air quality as “hazardous”, with a higher concentration of particles per million than cities such as Bangkok, Jakarta or Hong Kong.