State Highway 1 has reopened after a fatal car crash near Waipu, north of Auckland, this afternoon.

Another person sustained serious injuries in the two-car-collision south of Glenmohr Rd, police said earlier.

The incident took place around 5pm and the road was closed until just before 9.20pm.

Police anticipated the road would be closed for a "number of hours".

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Diversions had been put in place at SH1 and Kaiwaka-Mangawhai Rd to the south and SH1 and The Braigh to the north.

The Serious Crash Unit had been deployed to the scene, police said, and would investigate the circumstances of the accident.