A car crash has caused a two-kilometre traffic jam on the Sydney Harbour Bridge just before peak hour, with motorists advised to avoid the area.

The Transport Management Centre said three southbound lanes and one northbound lane were closed after the crash, which involved several cars.

One of the cars involved in the crash on Sydney Harbour Bridge. Credit:Melina Cruickshank

Bus and car commuters were warned to expect lengthy delays.

"Southbound traffic is queued for around two kilometres, and northbound traffic is also heavy," a TMC spokesman said.