One person is dead and five have been injured, three seriously, after single vehicle crash in Northland early this morning.

Police were alerted to the crash on State Highway 12 in Ruawai, 70 kilometres north-west of Wellsford, around 2.20am.

"One person died at the scene ... police are investigating the circumstances surrounding the incident.

St John Ambulance tweeted that they sent two vehicles to help.

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"[We] treated six patients and transported five patients to Northland Base Hospital."

Three had serious injuries and one each had moderate and minor injuries.

A helicopter was also sent to the scene, they tweeted.