Restrictions in Hong Kong have stifled what were once the largest vigils marking the anniversary of the bloody crackdown by Chinese troops on pro-democracy demonstrators, leaving cities like Taipei, London, New York and Berlin to keep the memory of June 4 alive.

Near Victoria Park, the previous site of yearly vigils, hundreds of police conducted stop and search operations, and deployed armoured vehicles and police vans.

Reuters witnesses saw more than a dozen people taken away, including activist Alexandra Wong, 67, who carried a bouquet of flowers, a man who held a copy of "35th of May", a play on the Tiananmen crackdown, and an elderly man standing alone on a street corner with a candle.

Police on Monday said officers took away 11 men and 12 women aged between 20 and 74 who were suspected of "breaching the public peace at the scene".

The United Nations High Commissioner for Human Rights called on Twitter for the release of anyone detained for "exercising freedom of expression and peaceful assembly".

China's Foreign Ministry said in a statement that "today's Hong Kong is moving from chaos to stability and prosperity along the right track of "one country, two systems".

"External forces" including the United States should uphold international law and stop "futile political manipulation" over Hong Kong to contain China, a ministry spokesperson said.

Hong Kong activists say such police action is part of a broader campaign by China to crush dissent in the city that was promised continued freedoms for 50 years under a "one country, two systems" model when Britain handed it back in 1997.

Security is significantly tighter across Hong Kong this year, with up to 6000 police deployed, including riot and anti-terrorism officers, according to local media.

Senior officials warned people to abide by the law, but have refused to clarify if such commemoration activities are illegal under a national security law China imposed on Hong Kong in 2020 after sometimes violent mass pro-democracy protests.

In a statement, police said some had been arrested for seditious intent and for "breaching public peace".

In Beijing, Tiananmen Square was thronged with tourists taking pictures under the watchful eyes of police and other personnel but with no obvious sign of stepped-up security.

In mainland China, any mention of the Tiananmen Square crackdown - where troops opened fire on pro-democracy protesters, killing hundreds if not thousands, according to rights groups - is taboo and the subject is heavily censored.

In democratically governed Taiwan, the last remaining part of the Chinese-speaking world where the anniversary can be marked freely, hundreds attended a memorial at Taipei's Liberty Square where a "Pillar of Shame" statue was displayed.

In Sydney, one of over 30 places in North America, Europe and Asia hosting commemoration events, dozens of demonstrators rallied at the Town Hall, chanting "free Hong Kong", while holding up yellow umbrellas, the symbol of pro-democracy protests since 2014.

Australian Associated Press