SYDNEYresidents waking to the sight and smell of smoke should prepare themselves for more hazy mornings.

A number of controlled burns are planned for bush areas around the city in the coming weeks, the Rural Fire Service says.

Smoke from a hazard reduction burn along Linden Ridge in the Blue Mountains drifted across Sydney's west and CBD early today, prompted calls to radio stations from concerned residents.

And the RFS says there are a number of controlled burns planned across the state throughout the coming weeks, including several on Sydney's outskirts, so people should not be concerned.

"People should start to expect to see more smoke," RFS spokesman Ben Shephard.

"It's necessary as we head toward the fire season."

The RFS and National Parks and Wildlife Service  conduct hundreds of controlled burns every year to clear bushfire fuel, like dry grasses and leaves, ahead of the start of the traditional bushfire season on October 1.

The NPWS says it has been making the most of the dry, sunny winter conditions recently and will be conducting dozens of hazard reduction operations in the coming weeks.

NPWS Regional Manager Geoff Luscombe said in a statement that those residents who may be more susceptible to smoke, such as asthmatics, should keep indoors and close windows during burning operations.