"They're still trying to work out how to get rid of that stuff. It's milk fat ... apparently even the vehicles they're using to pick it up with, they're skidding all over the place," Inspector Cornell Klussein of police northern communications said.
A witness at the scene said it was a "miracle" the driver survived the crash.
"It's gone basically 500m down the road, nearly gone over a bank ... he was severely trapped," he said. "It's going to cause absolute, total chaos."
He understood 35,000 to 40,000 litres of milk products spilled on the road.
The truck and trailer were badly damaged, he said.
"The cab's basically gone.
"It's an absolute miracle he survived," the witness said.
The Westpac Rescue Helicopter from Auckland landed on the highway about 100-200m from where the truck had come to a halt.
A spokesman said the driver was transported to Auckland City Hospital in a "critical but stable condition". NZME
