York Regional Police said they were called to the area of Yonge Street and Royal Orchard Boulevard at 1:15 p.m.
Police said the victim was on a York Region Transit bus travelling southbound on Yonge. The suspects were waiting for the bus to arrive and once it did, got on and the stabbing occurred.
The suspects then fled the scene on foot, police said.
There is no word on what may have led to the stabbing or if the suspects and the victim knew each other.
Police said they’re searching for two males, but didn’t provide a description.
The victim was taken to hospital with serious injuries.