State Highway 1 at Redwood Pass, Marlborough, is blocked following a crash between a car and a truck.
Emergency services were notified just after 10:30am.
One person is understood to be seriously injured, and a helicopter has been called.
The Serious Crash Unit has been advised.
Motorists are asked to use alternative routes as the road is likely to remain closed for several hours.
ENDS
Issued by the Police Media Centre