A SMOKE plume could drift as far as southwest Sydney today as firefighters backburn around a bushfire at Ku-Ring-Gai National Park.

The West Head Road bushfire has been burning near Pittwater since Friday, when a lightning strike is believed to have sparked the blaze.

The NSW Rural Fire Service said ground crews would be supported from the air as they begin backburning to strengthen fire containment lines at lunchtime.

"(We are) expecting a significant amount of smoke in the immediate area around the northern beaches, the central coast and the northern suburbs," an RFS spokesman said.

The smoke plume is expected to drift towards west and southwest Sydney later today.

The RFS said there was no threat to properties.

In the state's north, crews are still battling a 54,000ha bushfire burning near Coonabarabran.

Firefighters will spend today continuing the backburning they began yesterday.

Some 60 fires were burning around NSW today at an "advice" level.