One person has died - and at least 20 people have been injured - in a fatal crash between two cars and a bus in Otago

Emergency services were called to State Highway 6, north of Kingston just after 4pm.

One person in a car died at the scene, while two others are in a critical condition.

St John says it's treating additional patients with moderate and minor injuries.

State Highway 6 is closed between Kingston and Wye Creek, and motorists are being asked to avoid the area.

An eyewitness says a car had gone head-on into a bus towing a trailer.