Police have launched an investigation into how a milk tanker had its windscreen smashed and milk was poured across the road in Waikato at the weekend.
A police spokesperson said the incident happened near the intersection of Stokes Road and Orini Road, just north of Hamilton, at 1.20am on Saturday.
"The truck came to a stop where a group of cars and people were blocking the road," they said.
Video footage on social media showed the windscreen of the tanker being smashed with a hammer.
The driver's cab door was forced open, with people appearing to pull at the driver inside.
Significant amounts of milk can also be seen gushing onto the road.
"It is unclear at this time exactly what happened at the scene and the extent of the damage to the truck is yet to be established, though the driver is uninjured," the spokesperson said.
Fonterra have confirmed the tanker involved belongs to it and the driver is recovering.
"Our tanker driver was involved in an incident with members of the public on late Friday evening ... and we're supporting them through this. We're now working with police to resolve this matter."
Waikato mayor Allan Sanson said the attack happened after the tanker driver tried to push past a group of boy racers who were blocking the road.
Sanson said the tanker driver tried to nudge through the group and they took offence.
He said one of the group opened a valve on the tanker spilling the milk.
The area is a regular weekend haunt for boy racers, the mayor said.
Police said inquiries are ongoing and they are appealing to the public to help identify those involved.
"This behaviour is unacceptable, and police are committed to holding the offenders to account," the spokesperson added.
Anyone with information, video or pictures of the incident is being urged to fill out an online 105 report and quote file number 220320/4139.
Waikato police say they are running an ongoing operation to manage anti-social behaviour on roads.
In a statement, they said a significant part of the operation included working with local councils on environment design to discourage the activity.
In the past 12 months, Waikato police have confiscated more than 70 vehicles for offending relating to anti-social behaviour on roads.