It was the first time the vigil was banned in the global financial hub, with police citing coronavirus restrictions on group gatherings, as they did for all demonstrations last year. This year's protest is expected to face a similar fate.

Still, tens of thousands of people lit candles across the city in what was largely a peaceful event last June, bar a brief skirmish with riot police in one neighbourhood.

Commemorations of the Tiananmen crackdown are banned in mainland China, but Hong Kong traditionally held the largest vigils globally every year, having been promised certain freedoms when it returned to Chinese rule in 1997, including rights of expression and assembly.

Wong, 24, already in prison on other illegal assembly convictions and among 47 activists charged under the city's sweeping national security law, was sentenced in the district court on Thursday.

A 15-month sentence was cut to 10 after he pleaded guilty.

Judge Stanley Chan also sentenced Lester Shum, Jannelle Leung and Tiffany Yuen to terms of between four and six months. Twenty others facing similar Tiananmen anniversary charges are to appear in court on June 11.

"Freedom of assembly is not unlimited," Chan said.

Wong's longtime activist colleague, Nathan Law, who has fled the city and lives in Britain, condemned the sentence, saying the decision to ban the vigil last year was "unjustifiable".

"The court keeps increasing the length of imprisonment for protesters and sees it as a pathway for a society with fewer conflicts," Law said in a statement.

"It’s wrong — the only way to achieve harmony is to hold the powerful accountable. Now the courts are turned into weapons against the powerless."

The anniversary struck an especially sensitive nerve in the former British colony last year, just as Beijing prepared to introduce the new security law, which prescribes terms of up to life in prison for anything China sees as subversion, secession, terrorism or collusion with foreign forces.

This year, the anniversary event is particularly awkward for Beijing, which is celebrating the 100th anniversary of the Communist Party.

When asked if commemorating the victims of Tiananmen would violate the new security law, Hong Kong leader Carrie Lam last month said it was important to show respect to the Party.

China has never provided a full account of the 1989 Tiananmen Square violence. The death toll given by officials was about 300, most of them soldiers, but rights groups and witnesses say thousands of people may have died.

Wong received a 13-1/2 month sentence in December over an anti-government rally on June 21, 2019 and a further four months over an unauthorised protest in October 2019 while also breaking a government law against wearing masks.

While in prison, Wong was arrested in January on suspicion of breaking the new security law, introduced in July 2020, by taking part in an unofficial vote to pick opposition candidates for a since-postponed election, which authorities called a "vicious plot" to "overthrow" the government.