Tens of thousands of Hong Kongers braved thunder and torrential rain to attend a candlelight vigil Tuesday marking the 24th anniversary of China's bloody Tiananmen crackdown, as Beijing blocked commemoration attempts.

A crowd packed the former British colony's Victoria Park in an annual act of remembrance for the hundreds, perhaps thousands, of people killed in the June 3-4 onslaught in Beijing in 1989.

In the Chinese capital police blocked the gate of a cemetery housing victims of the crackdown on pro-democracy demonstrators as part of a sweeping annual attempt to bar commemorations.

In a narrow street near Beijing's Forbidden City, security personnel patrolled outside the former house of Zhao Ziyang, the former communist party secretary who was purged and held under house arrest for perceived sympathy with the protesters.

Mainland authorities also blocked online searches for a wide range of keywords ranging from "Tiananmen" to "candle".

Hong Kong and Macau, which reverted to Beijing's rule in the late 1990s but have semi-autonomous status, are the only places in China where the brutal military intervention is openly commemorated.

"Vindicate June Fourth!" protesters shouted as they huddled under umbrellas and rain doused candles. "We will never forget," they yelled.

The rally ended earlier than planned when loudspeakers stopped working.

"The candlelight vigil tonight has an additional meaning of not just condemning the massacre 24 years ago but also condemning the suppression today (in mainland China)," Lee Cheuk-Yan, chairman of protest organisers the Hong Kong Alliance in Support of Patriotic Democratic Movements of China, told AFP.

Billy Li, a 28-year-old recent university graduate, said he was attending because the Tiananmen protest "has not been vindicated, because the truth has not been told".

Organisers said 150,000 people attended the vigil while police put the number at 54,000.

"In order to love the country and the people, we have to continue to vindicate June 4th... fight against dictatorship and fight for a democratic China," Lee said in a speech at the vigil.

Pan Xidian was one of a number of mainlanders attending.

"I hope the next generation will not have to suffer the red terror, " the 42-year-old construction worker from the southern city of Xiamen told AFP.

"We have not given up."

Pan had travelled to Hong Kong for the first time to commemorate the crackdown that ended weeks of nationwide pro-democracy protests.

Beijing has never provided an official final toll for the military repression, which was condemned worldwide. Independent observers tallied more than 1,000 dead in Beijing, without including victims elsewhere.

In another development, the former mayor of Beijing who was believed to have played a prominent role in the Tiananmen crackdown died Sunday at the age of 84, it was reported late Tuesday.

Chen Xitong died in Beijing on Sunday morning, according to Hong Kong China News Agency, an outlet linked to the state-run China News Service.

Chen, who fell from grace in one of China's biggest political scandals in 1998, said he was "sorry" for the tragedy and that the deaths could have been avoided in an interview contained in a book released last year titled "Conversations with Chen Xitong".

He also attempted to shift the blame, saying he was merely acting on orders from the top leadership.

The Chinese Communist Party branded the Tiananmen protests a "counter-revolutionary rebellion" but pro-democracy advocates in Hong Kong have marked the event every year.

The protest also draws on discontent within Hong Kong under its Beijing-backed government, including corruption scandals, sky-high housing prices and a growing wealth gap, as well as slow progress towards democracy.

The city's leader is chosen by a pro-Beijing elite and the legislature is only partially elected.

China has promised to let Hong Kong people elect their leader by 2017 and to vote for all legislators in 2020, but no details have been given.

A survey of 1,000 people conducted by Hong Kong University last month found 68 percent thought the Chinese government acted wrongly in 1989, and the same number believed the city should spur the development of democracy in China.