Two patients have been choppered to hospital, after a serious crash between a truck and a ute north of Kaikoura about 9.30.
State Highway One is closed near Clarence, with initial police reports saying a truck and a ute have collided.
A St John spokesperson says one person with critical injuries has been taken by helicopter to Wellington Hospital.
She says the other patient with serious injuries has been flown to Christchurch Hospital.
Steven Mann, senior travel information advisor of the Christchurch Transport Operations Centre said the crash was located near Clarence Valley Rd, just north of Clarence itself.
"Caution is advised for travellers taking this route," Mann said.