Thousands have marched in Hong Kong to mark the forthcoming 20th anniversary of China's crackdown on pro-democracy protesters in Beijing's Tiananmen Square.

Police said the march from a downtown Hong Kong park was attended by at least 4,700 people on Sunday. Tens of thousands more are expected to attend a candlelit vigil on Thursday.

The protesters, who were mainly wearing black and white to symbolize mourning, shouted anti-Beijing slogans and carried banners calling on the Chinese Communist Party to readdress the events of June 4, 1989.

Among the crowds in Hong Kong was Xiong Yan, a former Chinese student leader during the 1989 demonstrations, once dubbed as one of Beijing's "most-wanted".

Xiong, who lives in exile in the US, was admitted into Hong Kong on Saturday for the first time in 17 years.

He expressed delight at having made it back onto Chinese soil and told the cheering crowds that he felt like he had "returned home".

China still considers the Tiananmen protests "counterrevolutionary", but they are openly marked each year in Hong Kong -- in one of the few such events on Chinese soil -- because it is ruled under a separate political system.

Hundreds, possibly thousands of people are believed to have been killed in China's military crackdown on pro-democracy protests in 1989. There has been no official inquiry so the exact death toll remains unclear.

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