In the one small patch of China that nurtures memories the Communist Party wants buried, tens of thousands gathered Saturday night in Hong Kong to commemorate the 1989 Tiananmen Square massacre, galvanized in their orderly outrage by China’s current crackdown on dissent, the most sweeping in two decades.

Unlike on the Chinese mainland, where public discussion of the Tiananmen killings is taboo, this former British colony has made remembrance of the military assault on student protesters in Beijing an emblem of both its own freedoms and its Chinese patriotism.

“I came to show that what happened won’t be forgotten,” said Dickson Lau, a 26-year-old teacher. “I’m a patriot.”

Though governed by Britain until 1997, Hong Kong has a history of supporting political reform in China that dates back to the 1911 revolution, in which the last imperial dynasty, the Qing, was overthrown.

Hong Kong has mourned the crushing of the Tiananmen student movement each year since 1989 with a candlelight vigil, but Saturday’s commemoration in Victoria Park was one of the biggest in recent years, said Lee Cheuk-yan, chairman of the Hong Kong Alliance in Support of Patriotic Democratic Movements of China, one of the organizers.

In Beijing, authorities marked the June 4 anniversary by rounding up yet more of their critics, continuing an assault on dissent that activists say is the harshest since the immediate aftermath of the 1989 bloodshed.

China also repeated its oft-stated position that the case is closed on the events of 1989. “A clear conclusion has already been made concerning the political turmoil that happened in the late 1980s,” said Foreign Ministry spokesman Hong Lei, according to the official Xinhua New Agency.

The ministry responded angrily to a call Saturday by the U.S. State Department for “the fullest possible public accounting of those killed, detained or missing” and an end “to the ongoing harassment of those who participated in the demonstrations” in Tiananmen Square. This, said the Chinese spokesman, is “a rude interference in China’s internal affairs and its judicial sovereignty.”

In a quiet challenge to Beijing’s insistence that tolerance of dissenting views leads to chaos, Hong Kong protesters left virtually no litter and even scraped up candle wax that had dripped on the ground. Organizers estimated the crowd at 150,000 or more. Police put the figure at half that, but independent observers said it seemed larger.

Noting that most of the people in the crowd were young, including many who were not even born in 1989, Lee, the Hong Kong Alliance chairman, said the large crowd was “very encouraging as it shows we have passed the torch to a new generation.” He added that the recent arrest of artist Ai Weiwei and dozens of others had stirred widespread anger in Hong Kong and boosted turnout.

This year’s Tiananmen anniversary, which falls less than a month before the Communist Party’s 90th birthday and follows weeks of political ferment in authoritarian nations across the Arab world, has been particularly sensitive for China’s party.

“They are determined to drive out any form of criticism,” said Bao Pu, a Hong Kong-based publisher whose father, Bao Tong, served as a senior adviser to Zhao Ziyang, the Communist Party chief who was deposed in 1989 for opposing the use of military force against protesters.

Bao Pu said his father, who spent years in jail after the 1989 killings, had been “invited” to leave Beijing on June 1 and been taken to a hot springs hotel to prevent him having contact with journalists or issuing statements during the anniversary period.

With details of the 1989 student protests erased from official Chinese histories, many young people on the mainland have little or no knowledge of the biggest pro-democracy movement since the 1949 Communist revolution. A new national museum dedicated to China’s modern history on the edge of Tiananmen Square makes no mention of Zhao, the ousted party chief who helped run China for nearly a decade and paved the way for its current economic success — but who became a non-person after he sided with students in 1989.