Hong Kong police detained an artist on Monday night after he appeared to write “8964” in the air with his hand, a reference to the date of the Tiananmen Square massacre, hours before Tuesday’s 35th anniversary.

Public acknowledgment of the events of 4 June 1989, when Chinese soldiers shut down a weeks-long peaceful protest with violence, killing anything from several hundred to several thousand people – is banned in mainland China and increasingly sensitive in Hong Kong.

The artist, Sanmu Chen, was standing outside Causeway Bay station, surrounded by media when he made the apparent tribute to the massacre. He also mimed pouring wine on the ground, in a Chinese tradition mourning the dead.

Police officers soon arrived and moved him into a police bus. A Hong Kong Police spokesperson told the Guardian they received a report about a man “causing a disturbance”. She said he was taken to the police station for inquiries but was later released “unconditionally”.

Earlier tonight, Hong Kong performance artist Sanmu Chen appeared to sign the words “8964” in the air—referring to the date of the 1989 Tiananmen Square crackdown—before being surrounded and taken away by police.

Sources tell @AFP that Chen has been released. pic.twitter.com/0sdTgdLegO

— Holmes Chan (@holmeschan_) June 3, 2024

On Tuesday, Beijing’s Tiananmen Square was closed. A notice on the ticketing website said reservations to visit the area were suspended for the day, and previously booked tickets could be returned for a refund. A resident told Reuters the main thoroughfare lining the square, Chang’an avenue, was closed to cyclists and pedestrians.

There was no mention of the 4 June date in Chinese state media, but some China-based English-language accounts on X on Tuesday sought to spread claims that accounts of the massacre were western disinformation. Both X and discussion of 4 June 1989 are banned inside China.

Police search performance artist Sanmu Chen, left, after he traced the Chinese characters of ‘8964’, referring to the 1989 Tiananmen Square massacre. Photograph: Yan Zhao/AFP/Getty Images

However, diaspora groups have planned commemoration events around the world, including in the UK, Australia, the US, and Taiwan. Taiwan’s president, Lai Ching-te, on Tuesday paid respect to the “students and citizens who bravely marched for change”.

“The commemoration of June 4 is not only for the sake of June 4, but also because people around the world who care about democracy and freedom share a common belief: only democracy and freedom can truly protect the people,” he said in a statement shared across social media platforms.

“A truly respectable country allows its people to speak up.”

On Monday human rights groups said Hong Kong and Chinese authorities had arrested or put under surveillance several dissidents ahead of the date.

Hong Kong police have arrested eight people under a new national security law in relation to accusations they had posted messages with seditious intent ahead of an “upcoming sensitive date”.

A man in Washington DC holds a picture of the late Chinese dissident Liu Xiaobo during a candlelight vigil to mark the anniversary of the Tiananmen Square massacre. Photograph: Alex Wong/Getty Images

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. This week two Hong Kong legislators said it was still legal for people to mark the date privately in their homes.

Regina Ip, a pro-Beijing legislator, told the Hong Kong Free Press it was “high time” public commemorations stopped, because some people had “preyed on the emotions of the people and weaponised June 4 commemorations” to stir up hatred against the Chinese government.

However she said: “If a person does anything in private without the intention of inciting hatred of the government, I don’t think an offence is committed.”

Last week Debbie Chan, former pro-democracy legislator who now runs a small shop, said her business had been visited by police and three other government departments after it began giving away memorial candles. Chan said she had also been contacted by a police officer who asked if she was “going for a run” on 4 June, according to Hong Kong Free Press.

Years into the Hong Kong government’s crackdown, the city is now under far tighter control by the Chinese central government. Attempts to organise candlelit vigils across the city and in homes in previous years have resulted in arrests, and residents fear commemorating 4 June will soon become as difficult for them as it is for people in mainland China.

Additional reporting by Chi-hui Lin