Two people have been hurt in a multi-vehicle crash that caused major traffic problems on the Sydney Harbour Bridge this morning.

At least five vehicles were believed to have been involved in the accident.

Two people were treated for injuries at the scene.

All northbound lanes and two of five southbound lanes were closed after the crash, but all lanes have since been reopened.

Motorists were being advised to use other routes, creating traffic snarls banking for several kilometres on all approaches to the CBD.

City-bound bus services were terminating at North Sydney, and some services were delayed by up to an hour.

The crash caused major delays for northbound traffic. ( ABC News: Rachel Pupazzoni )

Sydney Trains said it would accept bus tickets for the metropolitan area to help commuters reach their destinations.

Vic Lorusso from the Australian Traffic Network told 702 ABC Sydney the crash happened just after 6:35am.

He said the traffic around the bridge was a mess and the closure had affected roads across the city.

"We're urging motorists to delay their journey into the city if at all possible this morning," Mr Lorusso said.

One of the injured people was taken to St Vincent's Hospital in a serious condition.

The other was in a stable condition and has been taken to Royal North Shore Hospital.