Crash investigators were examining the scene of a fatal accident on State Highway 1 on Sunday, at Koromiko south of Picton.
One person died in the crash, which happened after a ute carrying six teenagers left the road late on Saturday night.
A 17-year-old man died at the scene, while another 17-year-old man was airlifted to Wellington hospital in a critical condition.
The other four passengers, who were all under 18, were treated at Wairau hospital in Blenheim.
The road was down to one lane for most of Sunday while investigators from the serious crash unit examined the scene.