Two people are in a serious condition after a four-car pile-up which has closed State Highway 1 north of Auckland.

Police are attending the serious crash which happened at the intersection of Moir Hill Rd on SH1, between Puhoi and Warkworth at about 5.50am.

A third person received moderate injuries.

One patient has been taken to hospital by helicopter and the two others are receiving treatment at North Shore Hospital.

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NZTA confirmed SH1 is closed to southbound traffic at Warkworth and a detour is in place along SH16.

The road is expected to be open by 9am.