A serious crash has blocked State Highway 27 and diversions are in place.

Emergency services are at the scene of a two-car crash between Patetonga and Torehape on the western side of the Hauraki Plains.

One person was in a serious condition and has been transported by helicopter from the scene.

The Waikato Serious Crash Unit was in attendance.

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The road would require restoration following the investigation, police said.

Transport contractors are on site and the road will reopen as soon as possible.

Police are requesting drivers take alternative routes and take extra care while travelling.