State Highway One has reopened between Blenheim and Picton, after a serious three-vehicle crash at Tuamarina, about 6.30am

Police say one person was thrown from their vehicle, when it hit a wire barrier - and have been flown to Nelson Hospital, in a critical condition.

St John says two other moderately injured people refused transport to hospital.

The Transport Agency says a temporary speed reduction's in place - and is warning motorists of a slippery road surface.