State Highway 1 in North Canterbury has been closed after a serious crash involving two trucks, including a gas truck that rolled.
Emergency services were called to the scene, at Greta Road in Greta Valley, shortly before 9.15 this morning.
The driver of the Rockgas carrier is believed to be in critical condition, police said.
The Serious Crash Unit is at the scene and the road could be closed for some time, police said.
New Zealand Transport Agency has warned travellers in the area to plan for at least two hours of extra travel time.