One man has been arrested but it is feared two more suspects may have fled the scene.
Norris said he saw the driver of the van running toward a gate before being caught by a group of men.
"They beat him as soon as they caught him. So that's kind of the scenario I was presented straight away, was them grabbing the guy and just pummelling him to the ground really and then just continued to kick him and stuff," he told 1 News.
Norris described the men from the van as "white guys".
He told 1 News he believed it was an "anti-Muslim attack".
"It's right outside the mosque. Because it's right next to the mosque I think they were probably waiting for a chance to do it."
One person has been stabbed after a man armed with a knife leapt out of a vehicle near the mosque, the Evening Standard reports.