Cordons were in place, including at Old North and Oraha Rds, Riverhead and Koraha Rds and Oraha and Matua Rds.
Motorists are advised to avoid the area, if possible.
Meanwhile two people were in a serious condition after a multiple-car crash at South Auckland's Mahunga Drive off-ramp to State Highway 20 at 1.24pm today.
It is understood one person was trapped in a vehicle, and another one crashed into a fence.
St John treated five people, two of whom are in a serious condition and three in a moderate condition. The patients were taken to different hospitals.
The road has since reopened.
The occupants of a car that went down a bank in Lower Hutt this morning have escaped without injuryand a crash in Te Horo outside of Wellington snarled-up traffic, blocking the northbound lane of State Highway 1.
A helicopter was called after the crash, which happened shortly after 10am.