Truck breakdown on Sydney Harbour Bridge

A truck has broken down on the Sydney Harbour Bridge, causing significant delays for motorists heading to the city.

Traffic on Tuesday morning was queued back about 7km to the exit of the Lane Cove Tunnel, the Transport Management Centre said.

Response crews are on the bridge working to remove the truck which reportedly has a broken gearbox.

Motorists are being urged to delay their journey southbound across the bridge or allow plenty of additional travel time.

Bus services travelling citybound on the bridge are also affected.