"We should have done more": Teens describe encounter with Melbourne's accused car attacker.

Two teenagers filmed trying to stop the accused Bourke Street mall attacker as he drove erratically outside Flinders Street station have said they wished they did more.

Cousins Isaac Tupou, 17, and Tevita Mahina, 17, attempted to the halt the driver with a baseball bat before the rampage was carried out that killed at least five people and injured dozens more.

The Year 12 students were at Federation Square for a church youth group event on Friday when they saw a man driving in circles at the intersection of Swanston and Flinders Sts.

“We saw him doing doughnuts and screaming to the crowd and in that moment, I knew he was going to inflict pain or was going to harm someone,” Isaac told Nine News.

Isaac said he and his cousin decided to take action "because no one was doing anything" and, armed with a baseball bat they'd been playing with, raced towards the driver.

"The car came at us then I stepped to the side and swung the bat," Tevita told Nine News.

"Then he came back and chased us off."

Tevita and Issac expressed their regret at not being able to have done more to prevent the deadly attack.

"We should have done more," Tevita said.

Isacc added: "I wish I had something in my hand too and kept hitting."

A woman who captured footage of the pair confronting the driver told The Project she thought they were "pretty brave".

"I believe they were trying to stop him because at one point he stopped right in front of us and as he came around he nearly swiped them right off the road," Meesha Rhodes Ali said.

"When I saw that I just thought this guy is out to kill someone. We didn't know if he had a weapon with him, if he was going to pull out a gun... It was really crazy."

The man allegedly responsible for the attack, Dimitrious Gargasoulas, is under police guard in hospital, but will likely face multiple counts of murder when he is charged.