Police gave him two warnings before opening fire. When he tried to strike the victim again, an officer shot him from about a metre away, Tsang added. The bullet struck the right side of his chest.

The supermarket manager sustained injuries to the back of his head. Both the men were sent to nearby Kwong Wah Hospital, where the attacker was certified dead at 1.21pm.

“According to our initial investigations, a few minutes before the attack, there was a dispute between the manager and the suspect. The suspect then left the scene, found a knife nearby and went back into the store to attack him,” Tsang said.

Surveillance footage obtained by the Post from a fruit stall located a block away from the supermarket showed the man, wearing a light-coloured T-shirt and black sneakers, running along Saigon Street at around 12.26pm.

He paused momentarily before swiping an object off a table outside a Chinese barbecue restaurant and ran off with it. He then turned onto Reclamation Street where the supermarket was located.

Seconds later, two officers jumped out from a police vehicle arriving at the junction of Saigon Street and Reclamation Street and gave chase.

Police were investigating the suspect’s motive and whether it was necessary to use a gun.

Under the Police General Orders, officers are allowed to open fire in three circumstances: to protect anyone – including themselves – from death or serious injury; to bring about the arrest of a person who has just committed a serious or violent crime; or to quell a riot or insurrection.

An officer would have to assess both their own safety as well as the safety of others in the vicinity before making a decision to shoot, said Lam Chi-wai, chairman of the Junior Police Officers’ Association.

“Under those circumstances, there is only one objective if the police were to open fire, and that is to make sure they are able to stop the attacker armed with a lethal weapon from causing more harm to others,” Lam said.

During training, police officers are taught to aim at large areas of the body, instead of the arms and legs so they are able to stop the attacker as quick as possible.

When asked whether it was appropriate for the officer to shoot inside a supermarket where it was likely to be crowded, Lam said: “There are many places in Hong Kong where there are lots of people. Only the officer in question would be able to make the assessment of whether it is safe under those conditions for everyone.”

“Having served on the front line for 30 years, I probably would have made the same decision if I were there,” he added.

A woman who runs a vegetable store outside the supermarket said the dead man had been a regular in the neighbourhood.

“He behaves weirdly and we know he steals stuff so we’re always careful of him,” said the woman, who declined to give her name.

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A supermarket staff member said he had noticed a man behaving suspiciously in the store some time before the incident, as if he were trying to steal something, according to Yau Tsim Mong district councillor Benny Yeung Tsz-hei, who cited information from police and witnesses.

The manager then shouted at the suspect, telling him to leave, said Yeung, speaking at the scene.

In November last year Hong Kong police faced criticism after an officer opened fire in a crowded public area. A policewoman shot an assailant in the abdomen after he came at her and a colleague with a blade at Sham Shui Po MTR station.

Police also drew criticism in July last year after officers fired two shots near a housing estate in Tuen Mun when a suspected triad member tried to run them down with a car.

The Post has contacted Kai Bo Food Supermarket for comment.