Crashes in Huntly and Papakura are causing delays on a day when heavy holiday traffic flows are expected to cause widespread traffic congestion.
NZ Transport Agency tweeted just before 2pm that a crash in Huntly has blocked State Highway 1 in both directions, with emergency services now on site.
Another crash under the Beach Rd overbridge blocked the northbound lane under the bridge just before 12.30pm, causing heavy congestion back to Ramarama.
A Police spokeswoman said three vehicles were involved in the nose-to-tail accident just before 12.30pm, "slightly blocking" the northbound fast lane. No one was injured.
The Transport Agency warned earlier today that heavy traffic was expected on roads between Auckland and Northland between 10.30am and 5pm northbound and between 11am and 9pm southbound.