UPDATED 9.45pm: State Highway One south of Timaru has been reopened following a crash which claimed one life and has left five people injured.

A person, believed to be a child, died in the accident just south of St Andrews, near Waimate, around 2.45pm.

Police say they will not release any details about the victim until formal identification has been carried out and next of kin have been contacted.

Of the five people injured, one is in critical condition in Christchurch Hospital, and another is in critical condition in Timaru Hospital.

Three other people have been taken to Timaru Hospital with serious injuries.

The Canterbury Police Serious Crash Unit has been examining the scene, and the road is now open again.