A truck has overturned tonight on State Highway One, closing the road and causing lengthy diversions.

Police Southern Communications said the only detour was the inland Kaikoura Road, which was unsuitable for heavy vehicles.

At least one person in the truck was thought to be injured but the extent of those injuries was not yet apparent.

At 10pm, emergency services were working to clear the crash scene in Oaro, near Kaikoura.

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At 11:45pm, a Police Southern Communications spokesman said the highway was still closed.