Organisers said as many as 150,000 people attended the vigil [AFP]
Tens of thousands of people have gathered in Hong Kong for a candlelit vigil to mark the 20th anniversary of the fatal crushing of the Beijing democracy protests in the Tiananmen Square, while police blocked any attempt of commemoration in mainland China.
Organisers said about 150,000 attended the vigil on Thursday, while police put the figure at 62,800.
"We will never forget June 4," the crowds in the Victoria Park chanted while singing remembrance songs.
Many of those attending were dressed in white, the Chinese colour of mourning, or wore specially-made T-shirts, some with images of tanks.
Activists and human rights groups say that thousands may have died when the military moved in against the student-led protests on June 4, 1989.
Xiong Yan, a student leader of the 1989 protests, had surprisingly been able to enter Hong Kong over the weekend. Other Chinese June 4 dissidents were turned away ahead of the anniversary.
"Hong Kong is a part of China and can influence China more than any country, more than any place," said Xiong, who was one of 21 people placed on Beijing's most wanted list in 1989.
While Hong Kong became part of China again when it was handed back from colonial power Britain in 1997, it maintains a separate legal system including the right to protest.
Hundreds of police and security forces were deployed throughout the day in Tiananmen Square in Beijing on Thursday.
Officers searched bags and even the pockets of thousands of Chinese and foreign tourists streaming through checkpoints to visit the giant square in the Chinese capital.
Foreign journalists, including Al Jazeera's crew, were barred from the area, although the square remained open officially.
China had prevented public discussion and remembrance of the events by blocking access to social networking websites like Twitter, and hiding away key dissidents.
The human rights group Amnesty International called on the Chinese government to hold a public inquiry into the crackdown.
"Hundreds of people were slaughtered, there are still people in prison 20 years later for peacefully demonstrating for their rights," said Kate Allen, Amnesty's UK director.
Ahead of the anniversary, Hillary Clinton, the US secretary of state, urged China's leaders to open up about what she called "the darker events" of the country's past.
She called on China to publish a full list of those killed or missing as a result of the crackdown, saying it would help China "learn and heal".
But the government in Beijing expressed "strong dissatisfaction" with such demands.
"On the political incident that took place in the 1980s, the party and the government have already reached a conclusion," Qin Gang, a foreign ministry spokesman, said.
Thousands of people commemorated the anniversary around the world.