A gas tanker has rolled and caught fire after colliding with a truck on State Highway 1 in Greta Valley, North Canterbury.

A St John spokesman confirmed one person had serious injuries and would be flown to hospital by a helicopter.

A freight truck collided with the gas truck near the intersection with Scargill Valley Rd and Valley Rd about 9.10am.

The gas truck had come to a stop on a grassy verge alongside the state highway and gas canisters had fallen around it.

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Hurunui District Council said nearby residents were reporting Fossil Point had been evacuated.

The area of SH1 near Omihi Rd is closed to all vehicles.

A detour is in place along inland Route 70.

Police have advised the road may be closed for some time and the Serious Crash Unit is attending the scene.

Greta Valley is about 83km north of Christchurch.