Fire crews have their work cut out for them with the blaze at Macquarie Park, following reports that the fire has jumped the road and has spread.
Four more crews are on their way to the scene to help the five crews already attempting to control the grassfire.
Traffic has been affected, with one northbound lanes of Lane Cove road closed in the Macquarie Park direction.
Motorists have been advised to allow extra travel time.
Earlier on Hit
It is understood that an emergency call was placed just after 11am today.
A spokesperson from Fire and Rescue NSW told Hit that the four hectare fire was contained at around 12.20pm this afternoon, but has not been extinguished.
A small back-burn is taking place to lock in the fire so it won't spread any further.
Residents are advised that there will be a large volume of smoke visible in the area for some time, due to the size of the fire.
Fire Investigation teams have been sent to the scene to determine how the fire started.