According to passengers on the bus, the victim, between the ages of 18 to 20, was sleeping with his head against the window when the attack occurred.
"He was listening to music when suddenly the person next to him began to stab him in the neck with... a large butcher knife," CTV's Murray Oliver reported Thursday from Winnipeg, Man.
Garnet Caton, who was sitting in front of the victim, heard the commotion and turned around thinking he was going to witness a fight.
Caton told CTV News that once he realized what was going on he screamed: "Stop the bus, somebody's getting stabbed, everyone get the hell off."
The bus driver pulled over on a section of the east-bound Trans-Canada Highway -- about 15 kilometres west of Portage la Prairie, Man -- and many of the 37 passengers began to flee the bus.
Canton gathered a small group of people to go back and help the victim, said Oliver.
"They returned to the back of the bus to find that the person who was stabbing the person in the neck had now sawed off the head of (the victim)."
The man, with the head in one hand and the butcher knife in the other, then tried to attack the other passengers, said Oliver.
The group was able to exit the bus and slammed the door behind them.
The man then stabbed the door with his knife but was unable to break through and get off the bus. Eventually, he attempted to start up the bus to drive away but the operator had hit a switch, disabling the vehicle.
Oliver said a truck driver then arrived at the scene and handed out wrenches and crowbars to several men. The small group gathered around the door to the bus and prevented the man from exiting until police arrived.
RCMP eventually arrested the man after a standoff lasting several hours, said Oliver.
Witnesses said the suspect was tall, large and wearing sunglasses, even though it was dark.
The bus was travelling from Edmonton to Winnipeg.
The RCMP and Greyhound officials have confirmed that a "major incident" took place on the bus but few details have officially been released.
This is just...
I thought this sort of thing only happened in R rated horror films. I feel semi-nauseous after reading this.
When the people had trapped him in the bus he taunted them by dangling the head out of the window. Seriously messed up.