A nine-car crash in heavy fog on Auckland's Greenhithe Bridge is causing some delay for north-bound motorists.

The multiple nose to tail collision occurred shortly before eight this morning.

A police spokesman said no-one was injured in the accident.

However, traffic was backed up to Squadron Drive on the Upper Harbour Highway as the site was cleared.

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He said police were currently in attendance.

Motorists were being urged to exercise caution and be prepared for some delays.

The spokesman said there was also still a bit of fog around impairing visibility.