A crash involving a truck and car is causing lengthy delays on Auckland's Southern Motorway.

Emergency crews are at the scene on State Highway 1 just after the Takanini off-ramp. The accident happened shortly before 9.30am.

A northern fire communications spokesman said the crash was a minor prang between a truck and smaller vehicle.

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No injuries were reported, he said.

However, congestion is building in the area and motorists are being told to expect delays as the crash is blocking the left southbound lane after Takanini.

The NZ Transport Agency is telling motorists to merge right and to pass with care.