Chinese and Hong Kong authorities have arrested or put under surveillance several dissidents ahead of the anniversary of the Tiananmen Square Massacre this week, according to human rights groups.

On 4 June it will be 35 years since Chinese soldiers shut down a weeks-long peaceful protest with violence, killing untold numbers of people, estimated from several hundred to several thousand.

Commemorative events are planned in cities round the world, including Tokyo, London, Taipei and New York – where a museum dedicated to the massacre was opened last year – but not in the country where it occurred.

The event has been banned from public acknowledgment in China, prompting those who want to commemorate or discuss it to find creative ways to get around censors to avoid persecution.

Human Rights Watch said several individuals connected to the 4 June remembrance had been put under surveillance or temporarily moved from their homes by authorities. Among them were Zhan Xianling, a founding member of the Tiananmen Mothers group of victims’ relatives, human rights lawyer Pu Zhiqiang, and Guizhou student leader Ji Feng.

Mentions of the anniversary are largely impossible on China’s strictly controlled internet and media. Even obscure references in photos, words, and dates are often blocked from social media posts.

Famous photographs, such as that of the “tank man”, are banned, but so too are images or mentions of yellow rubber ducks after the toy became a popular replacement image. In 2022, one of China’s most popular shopping influencers was abruptly taken off air after a cake shaped like a tank was briefly shown on his live stream.

In the lead-up to the anniversary, some platforms and institutions appeared to be removing any opportunity for errant memorial posts. On its Weibo account on Friday, World of Warcraft said its website would be undergoing maintenance from 3-5 June, and users would be unable to log in or leave messages. On Saturday, a high school in Shanxi issued a notice to staff telling them not to post on social media until notified, and that assembly and religious activities were banned on 4 June, according to Teacher Li, who runs an information-sharing and activism-monitoring account on X.

For three decades, the largest Tiananmen memorial event was held in Hong Kong, but under a tightening crackdown by the city’s government against the pro-democracy movement, that too has been banned. Attempts to organise candlelit vigils across the city and in homes have resulted in arrests.

Last week, Hong Kong police used a new national security law to arrest seven people, accusing them of publishing messages with seditious intent ahead of an “upcoming sensitive date”.

The police searched homes and seized electronic devices. “Those who intend to endanger national security should not imagine that they can avoid police pursuit anonymously online,” the police said.

One of the women arrested was already in prison. Local media identified her as Chow Hang-tung, a prominent barrister and human rights activist who has been jailed on other charges.

Chow’s case is the subject of a documentary that will be screened at a 4 June event in Japan on Tuesday. She had been an organiser of Hong Kong’s Tiananmen Vigils, with the since-disbanded Hong Kong Alliance in Support of Patriotic Democratic Movements of China. However, in December 2022, she and others were charged with “inciting others to take part in an unauthorised assembly”. Chow was acquitted, but that was then overturned by the court of appeal in January.

“The Chinese government is seeking to erase memory of the Tiananmen massacre throughout China and in Hong Kong,” said Maya Wang, the acting China director at Human Rights Watch. “But 35 years on, the government has been unable to extinguish the flames of remembrance for those risking all to promote respect for democracy and human rights in China.”

The introduction of two new national security laws since 2020 have driven a climate of fear and self-censorship in Hong Kong, where activists, media, and other say it is not clear where the red lines are for authorities.

In its most recent issue, Hong Kong’s Christian Times newspaper published mostly blank space on its front page. It also did not publish it online as usual, saying it could not because of “circumstances”.

In an editorial, the paper, which in the past has often published articles about the Tiananmen anniversary, said society had become “restrictive”, and it could only “respond to the current situation by turning paragraphs into blank squares and white space”.

“Even a prayer that originates from historical memories may arouse ‘concern’,” it said.

“Facing history honestly is not to perpetuate grievances, nor to smear and incite, but to give future repentance and reconciliation a solid foundation.”

Additional reporting by Chi Hui Lin