A man has killed and severed a head from a fellow passenger in a bus travelling across Canada.

Witnesses said that victim was stabbed 50 or 60 times by the man sitting next to him on a Greyhound bus travelling from Edmonton, Alberta, to Winnipeg, Manitoba.

The murderer then severed his head with a large knife, BBC reported.

The driver pulled over and passengers fled from the bus, bracing the door to keep the attacker inside.

A 40-year-old man was arrested after a stand-off lasting several hours and remains in police custody.

"All of a sudden, we all heard this scream, this bloodcurdling scream," passenger Garnet Caton told CBC television.

"The attacker was standing up right over the top of the guy with a large hunting knife - a survival, Rambo knife - holding the guy and continually stabbing him... in the chest area," Mr Caton added.

"He calmly walks up to the front [of the bus] with the head in his hand and the knife and just calmly stares at us and drops the head right in front of us," the passenger said.

"There was no rage in him ... It was just like he was a robot or something," he added.

The 40-year-old attacker was arrested by police.

The RCMP have not identified the suspect or the victim. The attack appeared to be unprovoked and it is thought the killer did not know his victim. [SOURCE: BBC]