A Vietnamese man traveling on a Canadian passport has been jailed for life for stabbing to death a convenience store owner who caught him stealing potato crisps.

Self-proclaimed monk Bui Van Cuong, 33, was unanimously convicted of murder by jurors after three hours of deliberation.

He had previously denied the charge, saying he was merely "borrowing" the food and would repay the owner in his "next life." High Court Justice Maggie Poon Man-kay handed down a life sentence to Bui who did not offer any mitigation.

Bui claimed he was instructed by a "demon" to wound Paul Cheng Ka-pui, 38, with a knife. He told Cheng at least six times "you are going to die" before stabbing him.

Cheng caught Bui stealing crisps in his 7-Eleven store on Pitt Street, Yau Ma Tei, on the evening of March 8, 2016, and the two started arguing during which Bui opened the pack and started eating. He also gave Cheng the middle finger.

After leaving the store, Bui stole a knife from a nearby Wellcome supermarket and returned 10 minutes later, shouting repeatedly "you are going to die."

Cheng was heard pleading: "I do not want to die" as Bui stabbed him.

"The force was so great the blade broke from the handle," prosecutor Philip Chau Ka-chun told the court.

Cheng was sent to Kwong Wah Hospital with a 7.5-centimeter wound on the right side of his chest. He was later transferred to Queen Elizabeth Hospital but died on March 14 from multi-organ failure and excessive bleeding, leaving behind a wife and a daughter.

Police arrested Bui the next day in a McDonald's shop in Jordan Street after reviewing surveillance camera footage.

Under police caution, Bui said he was "frustrated and angry" after being busted for "borrowing crisps," and hence decided to threaten Cheng with a knife. He did not intend to kill Cheng, but "heard the voice of a demon" telling him to stab the store owner. Bui added that he was not drunk.

He was initially charged with attempted murder and two counts of theft, but was later charged with murder.

Bui arrived in Hong Kong in December 2015 on a visitor's visa using a Canadian passport. He told the court he was a "monk," but also claimed to be a Christian and a Catholic. Bui also said he started believing in Buddhism six years ago.

He became a monk five years ago and flew to Hong Kong to "look for a temple." He visited one on Lantau Island but to his dismay he found out through his "magic eyes" that the monks there would "kidnap and rape women."

The court heard Cheng was a "sociable person" and that his death had saddened his neighbors. Some started fund-raising campaigns to help his family.