A grass fire in Lane Cove National Park caused heavy traffic delays in the Macquarie Park area on Wednesday.

The fire forced the closure of all northbound lanes and one southbound lane of Lane Cove Road around lunchtime, and despite all lanes reopening by 5.30pm, traffic issues continued until after the evening peak hour rush.

Authorities advised motorists to allow extra travel time and drive to the conditions, with a lot of smoke in the area.

Buses also experienced delays up to 50 minutes, and some routes diverted from Lane Cove Road.