A long stretch of State Highway One north of Auckland has reopened following a fatal crash early this morning.

The highway between Silverdale and Warkworth - a distance of 34 kilometres - was closed following the 4.50am crash.

However, police said just after 10am the road had reopened.

One person died and four others were seriously hurt in the two-car crash.

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The highway was closed so the injured could be treated and diversions put in place, police said.

"[We're] aware that the closure and diversions caused considerable disruption to traffic and we appreciate the public's co-operation and patience during this time."