Charges are likely for one of the drivers involved in a four-vehicle pile up, which included two articulated truck units, that closed State Highway 1 north of Whangarei for three hours.
Police at the scene near Hikurangi said it was lucky no one was seriously injured given two large vehicles were involved in the crash that happened about 8.20am yesterday.
Faced with a five-day wet spell police reiterated their road safety message and warned motorists to slow down in the wet and watch their following distances.
Following the pile-up traffic was diverted through Hikurangi until the road was opened again at 11.30am.
Senior Constable Devon Milner said an initial investigation indicated a south-bound truck and trailer unit carrying large bales of silage was waiting to turn right into Jordan Valley Rd.
As it was giving way to north-bound traffic two cars travelling behind the truck were involved in a nose-to-tail crash.
A following NZ Couriers truck and trailer then appears to have jack-knifed and the cab collided with the rear of the truck and trailer unit carrying the silage.
The single occupants of each car were taken to Whangarei Hospital with minor injuries. The truck drivers were uninjured. Investigations were continuing but it was likely charges would be laid.
Mr Milner said the crash was a timely reminder for motorists to slow down in the wet weather and watch their following distances.
The weather forecast is for rain until next Tuesday, with heavy showers in parts of Northland.
Mr Milner said after a long dry spell rain could turn the road into a "slippery soup" and motorists needed to take extra care.
Just 30 minutes after police were called to the Hikurangi crash police, fire and ambulance officers were directed south of Whangarei to a single vehicle crash on SH1 about 1km north of the Mangapai turnoff.
A car had gone off the road and down a bank where it was balanced just above a drain.
Firefighters used ropes tied to fence strainer posts to hold the vehicle steady while St John officers and firefighters freed the female driver and sole occupant of the vehicle.
She was lifted on to a stretcher, loaded into the St John ambulance and taken to Whangarei Hospital in a moderate condition.
Police were to interview the woman in hospital to get a clearer picture of what happened. The road surface was wet at the time.
Sergeant Tai Patrick, of the Highway Patrol team, said messages to slow down and watch following distances were well known but said driving to the weather conditions could save a life. With rain forecast police were bracing themselves for inevitable crashes.