China deployed its vast security apparatus on to snuff out commemoration of the suppression of pro-democracy protests around Tiananmen Square 25 years ago, flooding the streets with police as censors scrubbed the Internet clean of any mention of the crackdown.
Several governments including the United States urged China to account for what happened on June 4, 1989, comments that riled China, which has said the protest movement was "counter-revolutionary".
Exiled Tibetan spiritual leader the Dalai Lama used the anniversary to call on China to embrace democracy.
China has never released a death toll for the crackdown, but estimates from human rights groups and witnesses range from several hundred to several thousand.
Troops shot their way into central Beijing after demonstrators had clogged Tiananmen Square in Beijing for about six weeks. There were also protests in many other cities.
Taking no chances on Wednesday, police, soldiers and plainclothes security personnel enveloped Tiananmen Square, checking identity cards and rummaging through bags looking for any hint that people might try and sneak onto the square to commemorate the day.
Police escorted a Reuters reporter off the square, which was thronged with tourists, saying it was closed to foreign media.
Police also detained another Reuters journalist for trying to report on the anniversary in one of Beijing's university districts, releasing him after a few hours.
Public discussion of the crackdown is off-limits in China. Many young people are unaware of what happened because of years of government efforts to banish memories of the People's Liberation Army shooting its own citizens.
"They have covered up history. They don't want people to know the truth of what they did," veteran activist Hu Jia told Reuters from his home in Beijing, where he said police were present to prevent him from leaving.
"Nobody would have confidence in them if they knew what they did... They should have fallen because of what they did," he added, speaking by mobile telephone.
While the anniversary has never been publicly marked in mainland China, more than 150,000 people are expected to gather on Wednesday evening in Hong Kong for a candlelight vigil.
A large number of mainland Chinese are expected to join the event in the former British territory, which returned to Chinese rule in 1997 but remains a free-wheeling, capitalist hub. The vigil has been held in Hong Kong every year since 1989.
PROTESTS QUICKLY SPIRALLED
China's Foreign Ministry on Tuesday defended the crackdown, saying the government had chosen the correct path for the sake of the people.
The protests began in April 1989 as a demonstration by university students in Beijing to mourn the death of Hu Yaobang, the reformist Communist Party chief who had been ousted by paramount leader Deng Xiaoping.
The protests grew into broader demands for an end to corruption as well as calls for democracy.
Many Chinese would balk at the idea of mass revolution today. China is now the world's second biggest economy, with most Chinese enjoying individual and economic freedoms never accorded them before.
"I don't think it can happen again," said a Beijing resident who gave his family name as Xu. "China's system is certainly different from the West. The population is huge, 1.4 billion people. If you want to govern it well, it's not easy."
But Wu'er Kaixi, a leading figure in the pro-democracy movement of 1989, said Chinese people could rise up once more against the Communist Party in anger at anything from endemic graft to the country's badly polluted air, water and soil.
"Yes, you gave us economic freedom, but you are jumping in and looting us, robbing us of our future, corrupting the culture, our values and the environment," Wu'er Kaixi told Reuters ahead of the anniversary from Taiwan, where he works at an investment firm.
"All this has been clearly and widely expressed by Chinese people in the last two decades. This discontent will emerge into one thing one day: a revolution. I am sure the Communist Party is very well aware of this."
Rights group Amnesty International has said at least 66 people had been detained in the period leading up to the anniversary.
That includes prominent human rights lawyer Pu Zhiqiang and four other activists who were detained last month after attending a private meeting at an apartment in Beijing to discuss the crackdown, prompting concern in the United States and Europe.
The White House said in a statement that the United States continued to honour the memories of those who gave their lives on June 4, and called for a full accounting of what happened.
In democratic Taiwan, which China claims as its own, President Ma Ying-jeou said China should ensure that a "tragedy" like June 4 never happened again.
"If Chinese authorities can tolerate differences, not only can that raise the height and the legitimacy of those in power, but also send a clear message to Taiwan that political reform in China is serious," Ma said in a statement.
Japan, engaged in a bitter territorial dispute with China, used the anniversary to urge Beijing to respect human rights and the rule of law.
United Nations human rights chief Navi Pillay on Tuesday called on China to reveal the truth about what had happened 25 years ago.
Chinese Foreign Ministry spokesman Hong Lei expressed anger at the comments from the United States and the United Nations, saying they interfered in China's internal affairs.
In a daily news briefing, he also said the Dalai Lama had "ulterior motives" for his Tiananmen comments.
The run-up to the anniversary has been marked by tighter controls on the Internet, including disruption of Google services, and tougher than normal censorship of the popular Twitter-like microblogging service Weibo.
"This is the 1,008th post that I've had scrubbed today," complained one Weibo user, attaching a screen shot of a message received from censors telling him that his post reading "It's been 25 years since that event" had been deleted.