HONG KONG—Hong Kong police blanketed a busy shopping district late Saturday and stopped people entering a park that traditionally held a mass candlelight vigil on the anniversary of the 1989 Tiananmen Square Massacre, a memorial event that is now banned.

Much of the park was barricaded throughout Saturday, but hundreds of people quietly flowed around the park’s perimeter in the evening. Many who staged small acts of defiance were stopped and searched by police amid an overwhelming security presence. Occasional scuffles broke out.

Armed police took away at least four activists, the political party they belonged to said. One of them, who had written the words “commemorating June 4th” on his face mask—which are mandatory in public in Hong Kong Kong as part of anti-Covid measures—was arrested for allegedly inciting an unauthorized assembly. The other three were let go after questioning, according to the group.

Hong Kong’s police force said it arrested six people between 19 and 80 years old as of 11:30 p.m., including a foreign national. They were held on suspicion of possessing a weapon, obstructing police officers and inciting an unauthorized assembly. Police had warned of heavy jail terms for anyone gathering unlawfully, part of a national-security crackdown to eliminate political dissent.

The vigil to commemorate pro-democracy protesters gunned down by Chinese soldiers 33 years ago has been banned since 2020, with Hong Kong authorities in part citing pandemic restrictions. More than two dozen people have been jailed for taking part, organizing or inciting others to attend the vigil over the past two years.

Police officers contended with protesters Saturday outside Victoria Park in Hong Kong on the 33rd anniversary of the Tiananmen Square massacre.

Photo: TYRONE SIU/REUTERS

Placing an electric candle near the window of a nearby parking lot looking over the park at around 8 p.m., a woman surnamed Lau took a photo of it against the backdrop of empty football pitches that in the past were occupied by a sea of candlelights.

The 30-year-old said she used to attend the vigil every year until it was banned. She said she was searched by police as she headed toward the park, though they didn’t find the electric candle.

“I think it’s because they think even small sparks could start a prairie fire,” she said. Mourning for victims of the tragedy, she said, should not be something you need to do stealthily.

Lighting flames of remembrance was taken up by Western diplomats based in Hong Kong. Local consulates representing the U.S., Finland and the European Union were among those that posted images of lighted candles placed near their windows. The diplomatic missions of Australia, New Zealand, Poland and others shared photos of candles or made statements in memory of the 1989 massacre.

Since the candlelight vigil was banned, some observers showed images of candles on their phones.

Photo: LAM YIK/REUTERS

“As an eyewitness in Beijing during 1989 to a moment of history, each year on 4 June I reflect as well as remember,” Brian Davidson, the top British diplomat in Hong Kong, wrote on the consulate’s Facebook

account.

The actions ratcheted up tensions between China and governments in the West, which have been critical of China’s efforts to stamp out people’s freedoms in Hong Kong. Authorities in the city have jailed political opponents, outlawed street protests and forced critical media outlets to close.

“To the people of China and to those who continue to stand against injustice and seek freedom, we will not forget June 4,” U.S. Secretary of State Antony Blinken said Friday.

The office of China’s Ministry of Foreign Affairs in Hong Kong said it rejected what it called political tricks of the foreign missions, urging them to “stop playing with fire.”

Mentions of Tiananmen remain forbidden on mainland China. Users on China’s major social-media platforms such as Twitter-like Weibo,

Wechat and short-video platform Douyin found themselves unable to update or change their profile pictures and personal status on June 4, the day of the anniversary.

Activists and people who recently left Hong Kong organized dozens of June 4 memorial events from New York to London, including documentary and theater screenings as well as public gatherings.

Hong Kong’s Victoria Park vigil was for decades the biggest Tiananmen memorial event in the world. It was considered a touchstone of the city’s right to free expression and its turnout was sometimes taken as a barometer of dissatisfaction toward authorities—there was a huge turnout in 2019, just days before mass antigovernment protests broke out across the city.

Some years, tens of thousands of people attended and sang songs, watched historical footage from 1989 and listened to speeches denouncing China’s one-party rule made by activists, many of whom are now behind bars.

Ahead of the June 4 anniversary, Hong Kong Chief Executive Carrie Lam referred to the city’s national-security law, imposed by China in June 2020, and public-health restrictions when asked if it would be illegal to commemorate the 1989 massacre.

Police set up roadblocks around the area Saturday afternoon and hundreds patrolled around Causeway Bay, the district near Victoria Park. Officers wearing stab-proof vests frisked many throughout the day, using loudhailers asking people not to congregate, or risk getting fined under anti-Covid-19 rules on social gatherings.

Some weren’t deterred. A young couple walked with their mobile-phone flashlights switched on, even though the street was bright with storefront floodlights. A man wearing a black cap and mask held up an image of a candle displayed on his phone.

Police arrested Chinese dissident Lau San-ching for allegedly inciting an unauthorized assembly, according to the League of Social Democrats, of which Mr. Lau is a member. The 69-year-old appeared alone at Victoria Park near dusk. He was wearing a mask referring to June 4 and a shirt printed with the portrait of labor rights activist Li Wangyang, one of the leading figures at the 1989 student protests who died while under security surveillance in 2012. Mr. Lau was a political prisoner in China for 10 years until 1991.

Three other members of the group, including Chairwoman Chan Po-ying, were also led away by police in a separate incident but were let go after questioning, the political party said.

—Liza Lin contributed to this article.

Write to Selina Cheng at selina.cheng@wsj.com