Heavy holiday traffic heading north of Auckland has now eased.

Holiday goers escaping the city coupled with a massive diesel spill made it slow going north earlier today.

The New Zealand Transport Authority is warning State Highway 1 from Puhoi to Warkworth is heavy in both directions.

Sections of the highway are down to a slow crawl in the usual northern bottlenecks as holidaymakers journey to and from Northland.

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Motorists are being told to take the alternative SH16 route from Silverdale to Wellsford to avoid delays or expect to sit in queues.

The heavy traffic was not expected to ease until 5pm.

A stretch of state highway north of Warkworth is under a temporary 50km/h speed restriction after 200 litres of diesel spilled near the intersection of Goatley Rd in an early morning crash.