A two car crash has caused delays on the Northern Motorway north of Christchurch.

A police spokeswoman said they were advised at 5.25pm that two cars had collided on the Northern Motorway, blocking the right hand northbound lane.

There was no mention of injuries.

NZTA said the crash happened in the northbound lanes on the Waimakariri River Bridge on State Highway 1.

Traffic monitoring showed congestion was building for northbound traffic.

Police said tow trucks were on the way as of 5.45pm, and traffic was reported to be flowing ok at that point.

Road users are being asked to travel with care and follow instructions on signage in the area.