PERTH: Hazardous smoke blanketed Sydney on Thursday as wildfires burned across eastern and southern Australia.

Thick smog shrouded Australia’s most populous city, leaving its iconic skyline barely visible two days after smoke created serious air quality issues.

The New South Wales Rural Fire Service said the smoke from around 50 wildfires burning mainly in northern parts of the state. Air pollution levels were reading nearly 10 times higher than the national standard.

“The smoke is expected to continue for several days,” the fire service said.

Wildfires have destroyed more than 600 homes in Australia’s most populous state.

The annual Australian fire season normally peaks during the Southern Hemisphere summer, but has started early after an unusually warm and dry winter.

People with respiratory or heart conditions were advised to stay indoors and seek medical advice when necessary.

The fire danger has also spread with authorities issuing declaring high fire risk for parts of Victoria state to the south. It is the first time in a decade Victoria has been declared Code Red, with the highest possible fire risk and a statewide total fire ban.

Temperatures were forecast over 40C (104F) in the state’s north.

Melbourne, Australia’s second most populous city, is forecast on Thursday to hit 39C (102F) after falling just short of its hottest November minimum at 26C (79F) overnight.

Victoria Emergency Management Commissioner Andrew Crisp warned Victorians to be vigilant. “Given fires could start and move quickly, you won’t always receive a warning or be told what to do if a fire starts,” he said.

The fire danger was also elevated to “severe” in the island state of Tasmania off mainland Australia’s southeastern coast, while more than 40 wildfires have broken out in South Australia.