About 150,000 people braved thunder, lightning, torrential rain and wind for the candlelight vigil in Victoria Park to remember people killed in Tiananmen Square 24 years ago.
While the formal vigil was cut short by the downpour, many remained in the park to sing in praise of those who died.
Democratic Party founding member Martin Lee Chu-ming said the large turnout showed the "fire of democracy still burns in the hearts of many people."
He added: "I see many young people who were not born in 1989 at the vigil. I believe it is conscience that has encouraged them to come out."
After a minute's silence at the start of the vigil, floral wreaths were laid at the Monument to the People's Heroes set up in the middle of the park.
But then the rain short-circuited the sound system. While repairs were attempted, people joined in songs such as Flowers of Freedom.
But the problems meant messages from 1989 student protest leader Wang Dang, Tiananmen Mothers' member Lu Yanjing, and Li Wangling, sister of late mainland labor activist Li Wangyang, were lost.
Even with the schedule cut short, however, a large number remained and kept singing.
"Vindicate June Fourth!" people shouted as they huddled under umbrellas and rain doused their candles. "We will never forget."
One man spoke for many by declaring: "I'm staying. The heavy rain means nothing when we think of students who lost their lives 24 years ago."
A woman in retreat said: "The park is flooding, though I don't want to leave because I truly believe in this cause."
Organizer the Hong Kong Alliance in Support of Patriotic Democratic Movements in China said 150,000 people turned out - the same as last year. But police put the attendance at 54,000.
Whatever the actual figure, alliance chairman Lee Cheuk-yan said the huge crowd and the wet faces reflected the persistence of Hong Kong people.
"I believe we have shown the central government our spirit and made clear our call for the crackdown to be re- assessed," he said.
Across Victoria Harbor, about 200 people were in a vigil at Tsim Sha Tsui. This group was organized by activists who had criticized the alliance's preliminary slogan - it was later dropped - about loving the country, which they claimed did not represent the view of most Hong Kong residents.
Lee Cheuk-yan had also said earlier that one of the student leaders from 1989 would be in low profile at the vigil. He did not name the person, who "came from the United States but not at the invitation of the alliance."
Lee also accused Chief Executive Leung Chun-ying of avoiding the June 4 event by scheduling a visit to Shanghai.
He said he wanted to ask the chief executive about his conscience as Leung had in 1989 made a statement condemning the central government but now avoided the issue.
Before taking off for Shanghai, however, Leung said his trip was arranged last year.