State Highway 2 at Mount Bruce between Masterton and Eketāhuna in Wairarapa is down to one lane after a serious crash this afternoon.
Waka Kotahi said the single vehicle crash was reported about 12.45pm.
It said stop go traffic management is in place while the road is down to one lane around the intersection of Hiwitoru Road.
Drivers should expect delays until the crash scene is cleared.
Police and Wellington Free Ambulance have been approached for comment.