Hong Kong police have detained several people and Chinese authorities have restricted access to Beijing's Tiananmen Square on the 35th anniversary of the crackdown on pro-democracy protesters, as cities in Taiwan and elsewhere marked the date.
Chinese tanks rolled into the square before dawn on June 4, 1989 to end weeks of pro-democracy demonstrations by students and workers.
Television news images of a lone Chinese man in a white shirt standing in front of a column of tanks spread around the world and became the iconic image of the demonstrations.
Decades after the military crackdown, rights activists say the demonstrators' original goals including a free press and freedom of speech remain distant, and June 4 is still a taboo topic in China.
The ruling Communist Party has never released a death toll although rights groups and witnesses say the figure could run into the thousands.
In China-ruled Hong Kong, police officers tightened security around downtown Victoria Park where large June 4 candlelight vigils had been held annually before tougher new national security laws took effect in recent years.
Police took away several individuals in vans, including 68-year-old Alexandra Wong after she held up a bouquet of flowers and shouted, "The people will not forget!"
Others who lit up their mobile phones in the park at night were escorted away and searched by police.
Over the past week, eight people were arrested for sedition under a new national security law, including prominent activist Chow Hang-tung, stemming from what media said were online posts linked to June 4.
"There are still forces that attempt to undermine Hong Kong's stability and security," Hong Kong leader John Lee told reporters, without mentioning June 4 specifically.
In Taiwan, several hundred protesters held a vigil on Liberty Square in downtown Taipei, holding up small LED candles and laying flowers before an altar with the numbers 89 64.
"The more they try to hide this event, the more effort we should put in to remember it," said Juan Chung-hao, 33, a university researcher in the crowd.
Taiwan President Lai Ching-te and his government reject China's sovereignty claims, saying only Taiwan's people can decide their future.
"The memory of June 4th will not disappear in the torrent of history," he said in a post on the anniversary.
In Beijing, Chinese foreign ministry spokeswoman Mao Ning told reporters that China "firmly opposes anyone smearing China and using this (June 4) as a pretext to interfere in China's internal affairs".
An official website for the Tiananmen Tower overlooking Tiananmen Square posted a notice earlier saying it would be closed for the entire day on June 4.
Time slots for visits to the square were also not available for June 4 on its official WeChat mini-app.
Chang'an Avenue, a wide boulevard fringing the square where the "Tank Man" once stood, was closed to pedestrians and cyclists on Monday evening, a witness said.
Small groups of "stability maintenance" volunteers, or retirees with red armbands, have kept watch in central Beijing neighbourhoods since last week.
Guards have also been stationed on pedestrian bridges, a regular practice during politically sensitive periods.
On Chinese social media platforms, including WeChat and Douyin, users were unable to change their profile photographs, according to online posts and Reuters tests.
In the past, some online users have altered profile names and pictures with symbolic images such as candles around June 4.
