State Highway 1 was closed near Timaru on Wednesday after a logging truck tipped over.
Police said they were alerted to the crash, in which the driver sustained minor injuries, about 11am.
NZ Transport Agency Waka Kotahi said the highway was closed at Salisbury between Scarborough and Beaconsfield Rds.
An update at 12.40pm said the road was likely to remain closed for several hours.
A detour was available via Talbot and Beaconsfield Rds, but this route was not suitable for heavy vehicles.
Police said contractors had been called in to clear the scene.
