Police have released new footage showing the moments before a convoy of gang members assaulted a man on a Waikato Expressway last week.

The footage is part of police's continued plea to the public for more information about the incident which has left the 31-year-old victim in a stable but critical condition in hospital.

The video showed a red ute travelling north near Rangiriri before 5pm on Friday last week. Behind the ute, about 70 people on motorbikes were following close behind.

It's understood the riders were linked to the Tribesmen gang, who were returning to Auckland from Taupō where they had been meeting with other members from across the country.

A source told the NZ Herald one of the riders was clipped by the vehicle, and when the vehicle's occupants stopped to check on the rider they were attacked.

A convoy of about 70 motorbikes were trailing the red ute on the Waikato Expressway last week. Photo / Supplied

An eyewitness to the incident described the moment where the ute and riders clashed.

"I think the [ute] tried to pull over and he ran one of the head followers into the grass inside the motorway," they said.

"Then he pulled over and opened up his door, and I saw three or four of the front people get off their motorbikes and walk over to the ute."

The eyewitness said it hadn't looked like the ute intentionally cut off the riders, but had rather been trying to let them pass.

Another eyewitness told the Herald they saw medics working on a person lying on the side of State Highway 1, with their chest bare and medical equipment connected to it.

The person said the ute at the scene had three large holes punched into its back window.

It was formerly believed the occupant of the red ute was dragged from his vehicle by the riders, but police since confirmed the man exited the vehicle before the assault occurred.

Detective Inspector Graham Pitkethley asked the public for any dashcam or cellphone footage of the incident from those in the area at the time.

He specifically referenced commercial drivers who were often equipped with dashcams.

"We are grateful to all those people who have provided electronic footage to us," he said.

"We are still specifically seeking any imagery that captures the assault itself."

• Footage can be uploaded to https://rangiriri.nzpolice.org.
• Information can also be provided via 105 by quoting file number 220311/5636 or anonymously through Crime Stoppers on 0800 555 111.