Major delays are continuing on State Highway 1 north of Whangārei after a crash near Hikurangi on Friday morning.
While no one was seriously injured in the two-vehicle crash about 11.40am, the highway was blocked by debris and a large diesel spill.
St John treated four people at the scene, none of whom was seriously injured, a spokesperson said.
Firefighters from the Hikurangi and Whangārei brigades responded to the crash.
As of 1.30pm, when the highway reopened, traffic was backed up from Saleyards Road, south of Fonterra's dairy factory at Kauri, to a point north of Waro Limestone Scenic Reserve, on the northern side of Hikurangi.
Traffic through Hikurangi township was also at a standstill.
Emergency services set up a diversion via Jordan Valley Road and Apotu Road, for northbound traffic only, while they continued to clear the road and mop up spilled diesel.
A police spokesman said the highway had reopened at 1.30pm but the traffic backlog would take a long time to clear.