Police are also investigating.

Punches were thrown in a dangerous confrontation between a baying crowd and some guards.

"That outcome was unacceptable," Summernats founder and co-owner Andy Lopez told The Canberra Times.

He said the investigation had already begun. There were discussions with the security company to try to understand how a highly charged situation exploded into some violence.

Phone videos widely uploaded to social media show a punch being thrown at a guard and objects being thrown.

As the atmosphere grew more confrontational, at least one guard appears to have laid into Summernats attendees, arms flailing.

In a second scene, a guard appears to kick a man on the ground.

In a third scene, some guards attempt to defuse the tense situation, restraining a guard, but he then moves forward and swings a punch.

In a fourth scene, a bare-chested attendee ends up on the ground with a security guard above him.

After police arrived on the scene, one person could be heard saying "get the security guard".

Mr Lopez said, "What happened in the video is not what Summernats is about."

"We are as disappointed as anyone but we need to investigate to understand what happened and implement any learnings that we get."

He said the security company was "one of Australia's leading security agencies".

"They take this matter as seriously as anybody. They deliver major festivals all around Australia," Mr Lopez said.

He didn't have a time-frame for the investigation but said that it was already underway while events were fresh in people's minds.

Despite the fracas, Mr Lopez said this year's Summernats had been successful. By and large, he said, the behaviour of the crowd had been "fabulous".

"With all big events there are challenges with event management. We work with police and our security advisors to deliver a safe event, and, generally speaking, we delivered."

The conclusions of the investigation would be made public, he said. "We are a transparent organisation, and we will share what those learnings are as they come to hand."

ACT Policing said on Monday that it was still investigating the events.

Confrontations between security guards and attendees have happened before.

Last year, drunken patrons flooded over the concrete barriers and onto the cruise strip, turning it into a burnout pad and bullying security staff out.

ACT Policing wanted to hear from anyone who could throw light on the brawl. They were also seeking witnesses after two people allegedly assaulted a security guard at a pub in Braddon on Sunday morning.