UPDATED 9:55am: Heavy rain is preventing police entering Westland's Wanganui River, where a car plunged off a bridge yesterday afternoon.

The vehicle, believed to be red Toyota, was located in the river last night, but river conditions have hampered the recovery.

It is not yet know who, or how many people were in the vehicle when it left the road, but police are asking anyone who had people fail to turn up at accommodation last night to contact them.

State Highway 6 is currently open, but travellers should expect some delays.

A rescue helicopter was searching the river and the police dive squad and crash investigators have also been dispatched.