For decades, Hong Kong was the only place in China where the victims of the 1989 military crackdown on pro-democracy activists at Tiananmen Square in Beijing could be publicly mourned in a candlelight vigil. This year, Hong Kong is notable for all the ways it is being made to forget the 1989 massacre.

In the days preceding the June 4 anniversary on Sunday, even small shops that displayed items alluding to the crackdown were closely monitored, receiving multiple visits from the police. Over the weekend, thousands of officers patrolled the streets in the Causeway Bay district, where the vigil was normally held. They arrested four people for committing “acts with seditious intention,” and detained four others.

Zhou Fengsuo, a student leader in the Tiananmen Square protest movement, said that Hong Kong is now under the same “despotic rule” as the mainland.

“Back in 1989, we did not realize the mission of a democratic China,” said Mr. Zhou, now the executive director of Human Rights in China, a New York advocacy group. “Afterward, Hong Kong protests faced the same suppression, the same vilification and erasure of memories.”

In 1989, the pro-democracy movement in China drew huge support from Hong Kong, then a British colony. After the Chinese military cleared student protesters occupying Tiananmen Square, killing hundreds and possibly thousands, some student leaders in Beijing were smuggled to safety via Hong Kong.

Every June 4 for three decades, Victoria Park in Hong Kong was where Tiananmen Mothers, a group representing victims of the massacre, could openly grieve and express hopes for a freer China. The gatherings drew huge crowds of tens of thousands of people, even as in the past decade some of the city’s younger generation of activists questioned the relevance of the mainland-focused movement as they embraced a distinct Hong Kong identity.

But since China imposed a national security law on Hong Kong in 2020, virtually all forms of dissent have been criminalized in the city. Pro-democracy and antigovernment protests like those that roiled the city in 2019 have been snuffed out.

The authorities have paid particular attention to commemorations of the Tiananmen massacre. They raided a museum dedicated to it, removed books about the crackdown from libraries, and imprisoned organizers of vigils.

In the past two years, the authorities cited pandemic restrictions to bar all public memorials of the crackdown. Those Covid restrictions were lifted this year, but instead of a Tiananmen vigil, Victoria Park was occupied by a trade fair. The fair was organized by pro-Beijing groups to celebrate the 1997 return of Hong Kong to Chinese rule, one month ahead of that anniversary.

The imprisonment of vigil organizers has raised the question of whether Hong Kong would ever allow residents to peacefully mourn the victims of the Tiananmen massacre.

Hong Kong’s chief executive, John Lee, has avoided providing a clear answer, saying only that “everybody should act in accordance with the law and think of what they do, so as to be ready to face the consequences.”

But the arrests on Saturday left little doubt. Among those arrested were Lau Ka-yee, of Tiananmen Mothers, and Kwan Chun-pong, a former vigil volunteer; they were carrying pieces of paper saying they were on a hunger strike as individual mourners. Sanmu Chan, a performance artist, yelled “Hong Kongers, don’t be afraid! Don’t forget June 4,” as a crush of officers took him away. The police also detained a man and a woman who had carried chrysanthemums and worn white clothing, symbols of mourning.

In the lead-up to the anniversary, the authorities were targeting the smallest gestures of remembrance.

Debby Chan, a former pro-democracy district official, had posted a few photos on social media of electric candles she put on display in her grocery store last Tuesday. The police and representatives of three different government departments visited her several times because of that, she said. But she was undeterred.

“The more we’re not allowed to talk about it, the more they make these moves, the more I feel it is the right thing to do,” she said in a phone interview.

To Lit Ming Wai, a playwright, Hong Kong has a responsibility to preserve and pass down the memory of the crackdown, especially as it has been distorted and then erased elsewhere in China.

In 2009, she co-founded a community theater group called Stage 64, which sought to make the history of June 4 more accessible for young people in Hong Kong. The troupe’s most popular play is titled “May 35th” — a euphemism for June 4 that some people on the mainland use to refer to the crackdown.

“When we talk about June 4, we are not just thinking about Tiananmen Mothers. Even more, we are thinking of Hong Kong,” said Ms. Lit, who had been an M.C. at June 4 vigils from 2004 to 2014.

That play can no longer be performed in Hong Kong without risking prosecution. Now based in England, Ms. Lit is seeking to take the play overseas. The play was originally performed in Cantonese, and had its Mandarin debut in Taipei on Friday.

“For us Tiananmen survivors, losing Hong Kong — this very important place that shielded history and truth — is very painful,” said Mr. Zhou, the former Tiananmen leader. After the raid and forced closing of a June 4 museum in Hong Kong in 2021, Mr. Zhou donated several Tiananmen artifacts to a newly established permanent exhibit in New York, including a bloodstained banner, a tent and a mimeograph. A section was devoted to Hong Kong.

He added that he related to the wave of Hong Kong dissidents who had left the city: the pain of exile and their struggle to keep the movement alive while far from home. But their presence abroad was helping to keep the memory of the crackdown alive elsewhere, he said.

“On the other hand, many Hong Kongers are now passionately participating in June 4 activities around the world, increasing attendance threefold in some places,” he said. “There are now many cities that are starting to commemorate June 4 because of the arrival of Hong Kongers.”