HONG KONG - Thousands of pro-democracy protesters marched from Victoria Park on Saturday (July 1) afternoon to mark the 20th anniversary of Hong Kong's handover from British rule to Chinese, just a few hours after Chinese President Xi Jinping ended his visit to the city.

The Civil Human Rights Front, which organises the annual protest, said 60,000 people had taken part in the 3-km march which started shortly after 3pm at Victoria Park in Causeway Bay, and was to end at the government headquarters in Admiralty, the South China Morning Post reported on Saturday (July 1).

A police estimate of the turnout was unavailable.

However, the organisers announced at 5.30pm that a planned rally in Tamar Park in Admiralty was cancelled because of heavy rain.

Two key themes of this year's march were "reclaim Hong Kong" and "release Liu Xiaobo", the jailed Chinese dissident who was recently released on medical parole.

A family member of Chinese activist Liu, who is a Nobel Peace Prize winner, has said Liu's "time is limited" due to fluid building up around his stomach caused by liver scarring. The Chinese authorities on Thursday reportedly told US, German and European Union diplomats that Liu could not be moved to get medical treatment elsewhere due to his illness and that his family agreed he should be treated where he is.

Lam Wing Kee, one of the five Causeway Bay booksellers controversially taken into mainland custody in 2015, made a speech on the stage at the protest.

The abduction and detention of the booksellers based in Hong Kong had raised fears over China's interference in Hong Kong, which is supposed to enjoy a high degree of autonomy.

Lam, who returned to Hong Kong in June 2016 after being held captive by Chinese agents for eight months, on Saturday urged the mainland government to release Liu and his wife.

A coalition of pro-Beijing groups also held events at Victoria Park, while other opponents of the pan-democrats gathered in alleys nearby and condemned "anti-China elements", the Post reported.

Front convenor Au Nok Hin, who is a member of the Democratic Party, said that growing concerns over Liu and Beijing's recent claim that the Sino-British Joint Declaration "no longer has any realistic meaning" could spark more people to take to the streets.

China said on Friday that the 1984 Joint Declaration with Britain over Hong Kong, which laid the blueprint over how the city would be ruled after its return to China in 1997, was a historical document that no longer had any practical significance.

The pro-democracy marches have been held annually on July 1 handover day since 1997. In 2003, half a million protesters marched against a government plan to introduce an anti-subversion law.

Mr Xi warned in a speech on Saturday: "Any attempt to endanger national sovereignty and security, challenge the power of the central government and the authority of the Basic Law or use Hong Kong to carry out infiltration and sabotage activities against the mainland is an act that crosses the red line, and is absolutely impermissible."

His comment on national sovereignty has raised concerns that this will put pressure on the Hong Kong government to enact the anti-subversion law, which is opposed by Hong Kongers who fear it will curtail their freedom.

Wong Ting Kwok, 67, who has been taking part in the march for 20 years, told the Post he continued to come out every year to remind people that the mainland government made promises about the city's autonomy, but he said the political situation was getting worse.

"In the beginning we did have hope for change," he said, adding that those hopes have faded because of the situation on the mainland.

Sam Hui, 24, who had moved back to Hong Kong recently after years of living in Beijing and Britain, came to watch the protest.

The video editor and photographer told the Post he did not know why anyone would want to protest, adding: "It seems futile to me."