Diesel and whey have spilled into the Awakino River in Taranaki this morning after a milk tanker crashed into the waterway and overturned.
The crash happened on State Highway 3 at Awakino on the coast, 98km northeast of New Plymouth, just before 9am, a police northern communications spokesman said.
The driver was pulled from the truck "pretty badly hurt", he said.
Environment Waikato duty manager Rob Dragten said the regional council was helping emergency services deal with the diesel and whey leaking from the vehicle, which was sitting overturned in the river.
"We're not sure exactly how much material has gone into the river yet.
"But river users, especially those near the coast, need to be aware of the spill that is occurring."
The Automobile Association warned there could be long delays.
Workers would start to recover the tanker about midday and motorists should try to use SH4 if possible.