Fire and Rescue NSW (FRNSW) reported on Sunday night that the fire was burning in the Lane Cove National Park on Sydney's northern outskirts.
A FRNSW spokesman said the blaze was near houses on Yanilla Avenue and Morona Avenue but was not posing any danger to homes.
He said 11 fire trucks and 50 firefighters were at the scene and had brought the blaze under control.
'We've got those fire crew surrounding the fire and are extinguishing it,' he said.
He expected favourable weather conditions would aid the operation in the next few hours.
'It's under control now, it's a matter whether we can full extinguish it,' the spokesman told AAP.
'I'd say we will, we've got favourable weather conditions.'
The spokesman advised anyone in the area suffering from the effects of smoke to stay inside.
He also said locals should contact emergency services if they believed smoke was coming from another fire in the area.