State Highway 8, north of Omarama, remains reduced to one lane after a truck and trailer unit rolled early this morning.
Emergency services hope to have the road cleared by about 5pm.
Constable Nayland Smith, of Omarama, said at about 3.30am, a truck and trailer unit, heading south from Christchurch to Cromwell, crashed on Omarama-Twizel Rd, about 2.5km north of the Omarama township.
''The truck which was carrying building supplys, crossed the centre line on a fairly straight stretch of road and went down a slight bank before rolling onto it's side, blocking the nothbound lane,'' Const Smith said.
The male driver was the sole occupant and was transported by ambulance to Timaru Hospital with a moderate head injury.
''At this stage it is too early to establish what the cause of the crash was,'' Const Smith said.
While State Highway 8 was reduced to one lane, traffic delays were minimal, he said.
