At least one person is believed to have been seriously injured after two vehicles collided in South Otago this morning.

A police spokeswoman said the collision occurred just before 10.30am near the intersection of State Highways 1 and 8, about 3km south of Milton.

"Two helicopters have attended, and at least one person is thought to be seriously injured."

SH1 is closed and diversions are in place, she said.

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The Serious Crash Unit will attend the scene.