Sydney has woken to a blanket of smoke this morning caused by hazard-reduction burns being done in preparation for the start of bushfire season.

And it’s not the first time this has happened – in August last year the air quality was compromised for the same reason.

The NSW Rural Fire Service tweeted on Friday “firefighters across NSW are taking advantage of favourable weather to conduct important hazard reduction burns [to] benefit hundreds of homes at risk of fire.”

According to the Office of Environment and Heritage the burns are taking place at Manly’s North Head and in Garawarra State Conservation Area in Helensburgh, just south of Sydney. Smoke will clear as the day continues but won’t completely dissipate until tomorrow’s rain and stronger winds.

The south-west and north-west of Sydney have been most affected by the burns; air quality rated as “hazardous” in both areas according to the NSW Office of Environment website.

The website is advising people in these areas, “especially people with heart or lung disease, [to] avoid outdoor exertion and stay inside as much as possible.”

In Sydney’s east the air quality was rated as “poor” at 8am this morning and the rest of the city was rated “fair” or better.