Traffic is backed up on Auckland's Southern Motorway after a truck rolled at the Newmarket Viaduct, sending debris across the road.
All lanes have reopened but traffic was heavy as rush hour began and motorist were warned to expect delays.
The unit rolled on the northboound lanes, blocking two of them at about 2pm, the New Zealand Transport Agency said.
Queues of traffic extended several kilometres in both directions after the crash.
Emergency services said no one was trapped in the vehicle or injured in the crash.
Newmarket Viaduct crashes in the past have turned into city wide snarlups.
NZTA said it woudl take time for queues to clear - particularly at a location like Newmarket which is one of the busiest sections of the Auckland motorway network. Other sections of the network may be affected as traffic builds up during the afternoon peak.