State Highway 1 was closed after a crash blocked lanes in both directions north of Auckland Monday evening, but delays remain.
Police said a truck travelling south crashed into a van about 4.49pm, closing the highway.
One person sustained moderate injuries and was being treated at the scene.
Waka Kotahi NZTA said the crash happened south of the Johnstones Hill Tunnel between Orewa and Puhoi.
Emergency services worked to clear the crash and reopen the road "as quickly as possible", the transport agency said.
Both northbound and southbound lanes have been blocked. The transport agency said a "lane shift" was in place, so traffic was limited to one lane each way on the northbound lanes.
Waka Kotahi is asking motorists to use the Hibiscus Coast Highway as a detour and to expect long delays.
Traffic southbound has backed up about 6km.
Meanwhile, a separate crash is blocking lanes further north on SH1 near Artillery Rd on the Brynderwyns.
Waka Kotahi said police were on-site, and asked motorists to follow their directions.
More to come.