Three people are missing after a car plunged into a river north of Blenheim overnight.

Marlborough's mayor is describing the crash where a car plunged into a local river north of Blenheim as heartbreaking.

A crane is now at the scene of a car crash in Tuamarina, where three people were unaccounted for after a car went into the river.

Police divers are joining the search for those missing after the car crashed off the road at the intersection of State Highway 1 and Bush Road and into the Tuamarina River at 1.45am on Sunday.

Two injured occupants were able to get out of the car to safety.

State Highway 1 was closed for some time but is now open, although there may be brief closures again later.

Mayor Nadine Taylor said her heart went out to everyone involved.

"It's an absolutely tragic event for whichever families and community it hits. It's going to be a heartbreaking day for some families somewhere when they receive this news, and it's life-changing news."

The two who escaped were transported to hospital with moderate injuries.

The Police National Dive Squad was expected to arrive in Marlborough around midday.