Diesel fuel has spilled into a river after a truck drove into a large slip on State Highway 2 in eastern Bay of Plenty.
Fire crews were notified of the slip covering the entire road at Waimana, south of Whakatane, just after 12.30am on Thursday.
Fire service spokesperson Jarron Phillips says there was a lot of rain in the few hours leading up to the incident and it was foggy when the truck drove into the slip and went down a bank towards the river.
Mr Phillips says the boulders that came down are described as being large as cars.
About 200 litres of diesel spilled from the truck's ruptured fuel tank, and some has gone into the waterway.
The truck driver was treated for minor injuries.
Most of the road remains blocked and drivers are being warned of delays.