Chinese communities around the world have marked the 15th anniversary of the Communist Party's 1989 Tiananmen Square crackdown on pro-democracy protesters.
Security was stepped up around the Beijing square
The day was not marked officially in mainland China, though a handful of protesters were arrested at the square.
In Hong Kong, thousands of people waved candles in memory of the dead and called for faster moves to democracy.
A US-based human rights group called on China to release 24 people jailed for their part in the protests.
The group, Human Rights in China, says the protesters were found guilty of hooliganism for offences such as carrying and handing out matches.
Ahead of the anniversary, activists in China and government critics were reported to have been put under house arrest or forced to leave Beijing.
1989 TIANANMEN EVENTS
15 April - Reformist leader Hu Yaobang dies
22 April - Hu's memorial service, thousands call for faster reforms
13 May - Students begin hunger strike as power struggle grips Communist party
15 May - Soviet leader Mikhail Gorbachev visits China
19 May - Zhao Ziyang makes tearful appeal to students to leave
20 May - Martial law declared in Beijing
3-4 June - Security forces clear the square, killing hundreds
Leading Chinese doctor Jiang Yanyong and prominent activist Liu Xiaobo are among several potential critics who have gone missing.
Tiananmen Square was quiet on Friday. A few people were hustled away to police vans after making small protests - including a man of about 50 who kneeled to pray in the centre of the square, according to a journalist on the scene.
The Associated Press news agency said at least 13 people were detained.
Universities were monitored to prevent commemorations taking place, and other activists reported being kept under surveillance.
These moves show how anxious the government feels about the anniversary, says BBC Beijing correspondent Louisa Lim.
There has been a recent increase in signed petitions calling for the government to reassess 4 June 1989, when troops opened fire on unarmed protesters around the square leaving hundreds dead.
The human rights organisation Amnesty International has also called for an independent inquiry, saying those found responsible should be tried and brought to justice.
But our correspondent says that China's rhetoric and its moves to silence its critics indicate there is virtually no chance of an imminent change to its official stance on the Tiananmen killings - that they were a necessary response to a counter-revolutionary riot.
In fact, there are even reports that Chinese officials have been ordered to watch a new documentary on the demonstrations, to persuade them that the crackdown was the only option available.
The annual candlelit vigil in Hong Kong's Victoria Park was the only official event on Chinese soil to mark the 1989 massacre.
Organisers said up to 60,000 people were expected to attend the event.
Pro-democracy supporters said this year's event would be highly charged as it comes amid fears the former British colony is losing its freedoms.
China sparked anger in the territory when it ruled in April that the Hong Kong people could not directly elect their leader in 2007.
"This year it's important for people to show they will not be silenced," said Law Yuk-kai, director of the Hong Kong Human Rights Monitor.