Traffic entering the Northern Distributor at Bulli is being diverted after a car accident.

The on-ramp to Memorial Drive has been closed to southbound traffic since 11am, with cars being directed to travel through Woonona to return to the distributor at Campbell Street.

It is believed an oil slick on the road caused a car to spin out and crash.

Emergency services and Roads and Maritime Services are in attendance, warning of "moderate traffic conditions" and that there is oil on the road.

Motorists are advised to exercise caution, reduce speed and allow extra travel time.

A two car crash which earlier closed one lane on Five Islands Road, Port Kembla, has been cleared.