There were large spots of what appears to be blood near the figure, as were a pair of men's black lace-up shoes.
Mr Hair said two civilians became involved as well as two police, trying to stop the man from his attack.
Dozens of police cars are on the scene with helicopters overhead.
Another said they heard "what sounded like a bomb and gun shot". Police response was swift and overwhelming.
The incident occurred on Bourke Street just outside the Target Centre, near the intersection of Swanston St. I heard at least one gunshot initially, ' one said.
Paul Pogba welcomes Manchester United underdogs tag
Lukaku's injury means he is a doubt for Sunday's trip to Manchester City, so Sanchez might get another outing at the Etihad. He added: "I think it's always good to be the outsider, so people expect bad of us and then we surprise people".
"People around me screamed that he had a knife but I couldn't see clearly from where I was", Meegan May said.
Olivier Giroud does not need to score, says Maurizio Sarri
Giroud told BT Sport: "It's true, I was hoping to score soon because I came back late from the World Cup and lacked a bit of luck. He added: "Today I was in trouble, too". "It's very important because then we can talk again about this competition in February".
United States proposes banning asylum through southern border
The new rule comes as a so-called caravan of migrants from Central America travels north by foot through Mexico to the US border. US Army troops enter a compound where the military is erecting an encampment near the US-Mexico border crossing at Donna, Texas.
AMD shows Zen 2-based 7nm EPYC Rome CPU in action
AMD's Mark Papermaster says the new Zen 2 cores offer double the throughput of Zen and twice the floating point performance. We have 2x performance per socket compared to the previous-gen EPYC processor, and this is an insane leap in performance.
Eddie Jones names his favourite All Blacks
New Zealand go into the game on the back of a 69-31 win over Japan in Tokyo last Saturday with a side featuring eight debutants. But there's a lot of good coaches out there. "You've got to play a certain way against them, there's no doubt about that.