Hong Kong held a candlelight vigil Monday to mark the 23rd anniversary of the Tiananmen Square crackdown, in stark contrast to mainland China where activists said hundreds of people were detained.

Hong Kong's Victoria Park glowed with candlelight in what has become an annual act of remembrance for the hundreds, perhaps thousands, of people killed in the June 3-4, 1989 onslaught against pro-democracy activists in Beijing.

"The trend of democracy cannot be blocked," Lee Cheuk-yan, chairman of the Hong Kong Alliance in Support of Patriotic Democratic Movement in China, told the crowd in a speech.

"Never forget June 4. Democracy for China now! Long live democracy!" he said, estimating that 180,000 people attended the event. Others said there were no more than 60,000.

Tiananmen veteran Fang Zheng, whose legs were crushed by a tank as the PLA rolled into the square said: "You have all not forgotten what happened 23 years ago. Thank you all for 23 years of support."

The former British colony is the only place in China where the Tiananmen Square crackdown is openly remembered, and the number of people attending the annual vigil has swelled in recent years.

People's Liberation Army soldiers stormed into central Beijing on the night of June 3, 1989, firing upon unarmed demonstrators and citizens as they ended six weeks of democracy protests on Tiananmen Square and around the vast country.

The anniversary of the brutal army action in the heart of Beijing is always hugely sensitive, but particularly so this year ahead of a once-in-a-decade handover of power marred by fierce in-fighting in the ruling Communist Party.

China still considers the Tiananmen demonstrations a "counter-revolutionary rebellion" and has refused to acknowledge any wrongdoing or consider compensation for those killed.

The government attempts to block any public discussion or remembrance of the events by hiding away key dissidents in the run-up to June 4, taking them into custody or placing them under house arrest.

Searches on China's popular social media sites for June 4, the number 23, the words "candle" and "Victoria" were blocked.

After the Shanghai stock market opened at 2346.98 points -- which some pointed out could mean the 23rd anniversary, June 4, 1989 -- censors responded by blocking searches for "Shanghai Composite Index" on the Sina microblog.

The United States called for all those still jailed over the demonstrations to be freed, but Chinese foreign ministry spokesman Liu Weimin hit back at what Beijing called "groundless accusations".

France joined the United States in calling for China to release political prisoners still jailed 23 years after the crackdown.

Despite the heightened security, public events have been held around the nation to commemorate the "Tiananmen massacre" and demand democratic reforms.

More than 80 rights campaigners met in a Beijing square on Saturday, carrying banners and shouting slogans calling for a reassessment of the 1989 protests.

"So many people were killed on June 4, we think the government should fully account for what happened," said Wang Yongfeng, a Shanghai activist who attended the protest.

A similar protest occurred in a park in southeast China's Guiyang city last week, with police subsequently taking into custody at least four of the organisers, the Chinese Human Rights Defenders group said.

In Beijing, veteran dissident Hu Jia said authorities had stepped up security around him and other political activists and social critics.

Rights activists and lawyers said police had contacted them and warned against participating in activities marking the crackdown.

The only open commemoration of the crackdown allowed on Chinese soil was in Hong Kong, a semi-autonomous southern territory that enjoys freedoms not allowed in the mainland.

Student Belle Shu Ting, 19, said she knew almost nothing about the Tiananmen crackdown until she came to study in Hong Kong from the neighbouring Chinese province of Guangdong.

"I learned about it in class and I found it be quite moving. I hope that this candlelight vigil will carry on until the June 4 event is vindicated," she told AFP.

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