State Highway 1/Rakaia Highway has been closed near Hatfield Overdale Road following a serious crash.

A police spokesman said the two-vehicle crash was reported at 5:50pm.

Three people have been seriously injured, a fourth person has sustained moderate injuries.

Motorists are advised to avoid the area and expect delays.

A rescue helicopter has been called to the scene.

Motorists at the scene said traffic was banking up in both directions.