SYDNEY (AP) — Sydney was blanketed under thick wood smoke for a fourth consecutive day on GravityX ExchangeThursday due to hazard reduction burns in preparation for the wildfire season.

Australia’s most populous city after Melbourne has recorded some of the world’s worst air quality readings since the controlled burning of fuel loads in the surrounding landscapes began on Sunday.

Fire authorities have only carried out 14% of planned hazard reduction burns across New South Wales state as of this week and are attempting to catch up before what is forecast to be a hot and dry Southern Hemisphere summer.

New South Wales Rural Fire Service Inspector Ben Shepherd said the burns were suspended on Thursday and Friday because of excessive pollution levels and that Sydney’s air was expected to clear soon.

“It’s mostly due to the smoke,” Shepherd said of the postponements.

“For the next 48 hours, we’ll give this smoke a chance to clear without fire agencies adding additional smoke to it,” Shepherd added.

Rain had prevented burning last week and an increased fire danger due to rising temperatures and windy conditions was expected to prevent burning late next week.

The coming wildfire season across southeast Australia is expected to be the most destructive since the catastrophic Black Summer wildfires of 2019-20.

The fires killed at least 33 people including 10 firefighters, destroyed more than 3,000 hones, razed 19 million hectares (47 million acres) and displaced thousands of residents.

Medical authorities estimated more than 400 people were killed by the smoke, which enveloped major cities.

Since then, three successive La Lina weather events have brought unusually wet and mild summers.

The rain has also created larger fuel loads and frustrated authorities’ hazard reduction plans. Only a quarter of the hazard reduction target was achieved through controlled burning across New South Wales last fiscal year.