The southbound lanes of the Northern Motorway in Auckland are closed at Silverdale a serious crash early this morning, police say.

One person was seriously hurt in the 2.30am crash and taken to Auckland Hospital.

"The Police Serious Crash Unit is investigating and for that reason the southbound lanes are closed and traffic is being directed off the motorway at Silverdale.

"The alternative route is the old State Highway One.

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The northbound lanes are open and police hope to reopen the southbound lanes by around 7am.