A Hong Kong man was jailed on Thursday for stabbing a police officer in the arm during protests against a Beijing-imposed national security law two years ago.

Wong Kwan-wa, 26, was sentenced to five years in jail after pleading guilty to rioting and wounding with intent, according to local media.

On July 1, 2020 – the day after Hong Kong's security law came into effect – thousands took to the streets in defiance of a protest ban, with police using water cannon, tear gas and pepper spray to disperse crowds.

Wong stabbed an officer in the upper arm when he was trying to arrest other protesters, an act which District Judge Frankie Yiu on Thursday described as "extremely serious."

The officer's injury could have been fatal as the knife wound was only 4 millimeters from his artery, the judge said, adding that the officer could no longer be on frontline duty.

The attack took place during a protest in the bustling Causeway Bay district involving around 300 people, which inconvenienced road users and the general public, the judge added.

Wong, a former civil engineer, tried to leave Hong Kong but was arrested in the early hours of July 2 on board a flight about to take off for London.

Hong Kong's national security law outlawed acts of subversion, secession, terrorism and foreign collusion, and offenders face a maximum penalty of life in prison.

It has been applied broadly, wiping out much dissent in the once outspoken city and leading to the arrest of many democracy advocates.

Beijing says it has restored stability to Hong Kong.

Police said seven officers were injured and more than 370 people were arrested during citywide protests on July 1, 2020.