A police spokeswoman said they are aware that a significant amount of milk was emptied from the tanker and a hammer was used to smash the windscreen.
Footage circulating online shows a man in a fluro yellow T-shirt holding a hammer. The video captures the man using the hammer to smash the window of the milk tanker.
"Police are aware that during the incident a significant amount of milk was emptied from the tanker and a hammer was used to smash the windscreen."
Police said the truck came to a stop at the intersection of Stokes and Orini roads where a group of cars and people were blocking the road about 1.20am on Saturday.
Earlier today, police said the driver was not reported to have been injured. "Police will be investigating and are in initial stages of inquiry."
There are disputed accounts over what caused the stand-off between the tanker driver and the young car drivers in Hamilton, with one person claiming the tanker failed to slow down as it approached the group of motorists blocking a road.
One social media user wrote the "disgusting" behaviour was why the "car community" copped "so much heat".
"I've been to plenty of meets where the truckers don't care and just wanna get [through].
There's no excuses, sort it out if y'all care about our future with cars."
One person told the Herald the tanker hit two cars and tried to drive off.
"The event had two groups of people attending. One group attacked the tanker while the other crew defended the tanker. The attacking group is not part of the normal car scene in Hamilton."
A young woman was reportedly injured as she tried to protect the tanker driver. "Another girl was reportedly shoved into nearby scrub and was stood on.
"The milk discharge was done by someone in the video who is clearly visible, this person has since been dealt to by his father.
"The tanker driver is a little shaken but unharmed thanks to the efforts of the local Hamilton car crew and their actions defending the driver and doing their best to stop the attack."
People information, video or pictures of the incident that could assist Police in identifying those involved are being asked to fill out an online 105 report and quote file number 220320/4139.