Two car crashes on an icy South Island highway have left seven people injured this morning.

State Highway 8 between Tekapo and Twizel has now been closed due to severe ice after a spate of accidents.

A man with serious injuries and a woman with moderate injuries were flown to Christchurch Hospital by helicopter when their car came off the road at 8.15am.

Just under an hour later a second car rolled on the same stretch of road.

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A St John Ambulance spokesman said five people in the car suffered minor injuries and were treated by staff at the scene and did not need to go to hospital for treatment.

A police spokeswoman said icy conditions had left the road treacherous to travel on with motorists struggling to keep traction.

There had been several minor accidents along the 55km stretch of highway and those who had managed to get through described the journey as extremely difficult.

The New Zealand Transport Agency closed the highway shortly after the second serious accident.