A motorcyclist who went under a milk tanker that caught fire in a crash near Ashburton this afternoon has died.

The State Highway has been closed for five hours around the corner of Maronan Road and State Highway One where the crash happened.

Emergency services were called just after two.

The man was taken from the scene in a critical condition to Ashburton Hospital but died soon after.

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The Serious Crash Unit's at the scene.

The NZTA expects the road won't be re-opened until 7 and detours remain in place.