Then a large truck and trailer carrying hazardous material crashed on Cove Rd, Mangawhai, the coastal highway being used as a diversion.
Police said that crash happened just after 9am between Woodleigh Lane and Bream Tail Rd.
Nothing was leaking from the truck but emergency services set up a safe space around the crash.
Fire Service northern communications shift manager Scott Osmond said the truck's dangerous cargo of ammonium nitrate was being carefully transferred.
The compound is predominantly used in agriculture as a high-nitrogen fertiliser. Its other major use is as a component of explosives.
Osmond said despite the crash the chemicals were still intact inside containers.
Four crews from Whangarei and Mangawhai were involved in the operation.
Meanwhile, SH1between Baldrock Rd and SH12 at Brynderwyn finally reopened to traffic after the first crash just before 1pm.
A crane was needed to move the overturned truck and trailer.
Traffic filing past the crash was earlier warned to expect long queues.
Police used stop/go signs to guide the building traffic through on a single passing lane.
It is not yet known when the coastal route will be reopened.
