The main route between Nelson and Blenheim is partially open following a crash between a logging truck and a car.
State Highway Six between Hira and Rai Valley was blocked due to the crash between a logging truck and a car about 3pm.
Police spokesperson Barbara Dunn said the female driver of the car was flown to Nelson hospital with serious injuries.
The road was initially closed but one lane had since reopened. However, a backlog remained and motorists should expect delays, Ms Dunn said.
Police investigators remained at the scene.