Hamilton paramedics were called to the mall on Centennial Parkway North at about 8:30 p.m., according to duty officer Ben Roth.
A male patient was taken to Hamilton General Hospital with potentially life-threatening injuries to his head and leg.
It is not clear how the man was injured.
"I can't confirm the nature of the injures," Roth said.
A heavy police presence, including a canine unit, remains on the scene.
Hamilton police said via Twitter shortly after 10 p.m. there is no sign of any immediate threat to public safety at the mall.