Videos posted on social media show members of the public restraining a man.
While other images show a man being led away by police.
One witness told the ABC he was walking towards Wynyard Park when a man came running around the corner "with a long knife".
"[He was] about three or four metres away from me, and then came about five or six other men chasing him," the witness said.
"They were armed with crowbars and one man had an axe and another man … I think had a firefighting implement.
"My immediate impression was that it was a scene from a crime show being shot, but then that quickly turned out not to be the case and the man ran down the road towards the cafe where patrons there must have tripped him up and they then put a milk crate over his head."