He said a man jumped out of one of the cars and started smashing the other car with a baseball bat. He said while this happened, another vehicle appeared and tried to run down another man.
"He got hit, but got up and ran off.
"I had to pull over because cars were all smashed up on the side of the road ahead of me. They even smashed through the bus stop signs and the arrow signs they have on the roundabouts."
The witness said it looked gang-related because he could see gang colours.
"It's just classic gang stuff. It's just so stupid."
The witness said he would normally be the type of person who would jump out and offer to help but he was in a hurry because of a family emergency.
He said he couldn't believe he was seeing such a thing in the middle of the day in Rotorua and admitted it felt as if his heart was in his throat.
"I was just like holy s***, I can't believe it."
A police media spokeswoman said the police were interviewing witnesses. She said all those involved had fled the scene and police were also trying to find the vehicles involved.
A Rotorua Daily Post reporter at the scene said the front and back windows of one of the vehicles involved was shattered.
She said patched members of the Mongrel Mob were walking around the area.
A Mongrel Mob member, who asked not to be named, described the scene as "utter chaos in the space of about 13 seconds".
"There was a fight between a lot of fellas and it just got out of control. People were crashing into each other, trying to run each other over and stab each other, I enjoyed it," he said.
"This is what we live for, this is what we breathe for."
The man said the incident had been going on over the space of a few hours and had started at a property in Kawaha Point.
"People entered the house to try and extract and kill the family, we got a call to intervene," he said.
"We the reds stabbed one of their members, then we took the lead car and used ourselves as targets to get them away from the family."
The Mongrel Mob left the property in three separate vehicles and the member said there were at least 12 of them.
"They hit our car off the road and we spun out, then they smashed us with baseball bats," he said.
The man said he has been a Mongrel Mob supporter since he was 12.
"It's in my blood," he said.
"There's more activity than there's ever been, this is only the beginning of it all, they think they've won, they haven't.
"They try to kill us, we will return the favour tenfold. Without a doubt."
Another local man who witnessed the crash said at first he thought it was just an accident until the Black Power members got out of their car.
"There was about six to seven of them, they had baseball bats," he said.
"They were trying to hit them and run them over."
Police are investigating the crash and the fight that followed.
Senior Sergeant Steve Shaw said it was "horrendous" for members of the public to witness such incidents.
"They [gangs] need to get over their taboos, sit down and talk to us," he said.
"This is what happens when they think it's best to just handle it their own way."
Rotorua police crime prevention manager Inspector Stuart Nightingale said the Mongrel Mob member's comments were an example of the gang being hell-bent on spreading community harm in any form it could.
"It's our mission to disrupt and dismantle organised crime such as the Mongrel Mob and Black Power," Mr Nightingale said.
"This kind of behaviour is unacceptable. We want to give real trust and assurance to the community that we are on top of this.
"The community in general is law abiding and should not have to accept this violence on our streets."
Mr Nightingale said two vehicles caught up in the collision were driven by innocent members of the public.
"We are following all leads of inquiry, stopping all gang-related vehicles and arresting anybody that is carrying a weapon," he said.
"Any form of violence is intolerable. We will be continuing an increased presence through the shifts to come and it will be reviewed again tomorrow."
Mr Nightingale said he wanted to hear from anybody who may have seen anything or captured any of the incident on a "dash cam".
He said police had arrested one man at the scene but were still looking for several others.
Anyone with information should contact Rotorua police on (07) 349 9400, or Crimestoppers anonymously on 0800 555 111.
