Hong Kong activist Joshua Wong held

Hong Kong - Hong Kong student pro-democracy campaigner Joshua Wong was detained by police on Wednesday after an anti-China protest ahead of a visit by President Xi Jinping.

Wong was among at least 20 protesters who had staged a three-hour sit-in at a harbour-front statue and were led away into police vans.

Xi's visit this week marks 20 years since Hong Kong was handed back to China by Britain and comes at a time when fears are growing that Beijing is tightening its grip on the semi-autonomous city.

Protesters had encircled the sculpture of a golden bauhinia flower which became the emblem of Hong Kong in 1997.

The statue was given to the city by China as a present to mark the handover.

Some activists chained themselves to the sculpture while others climbed into its petals.

Police cleared the area and surrounded the statue, leading away protesters one by one.

Most walked, but Wong and young legislator Nathan Law lay down and were carried away from the scene.

Police had warned the protesters they were causing a public nuisance and would be arrested if they did not move.

Some demonstrators remain on top of the statue, with at least one chained to it.

As Wong was carried away to the awaiting vans, he shouted: "Protest on July 1!" - the anniversary of the handover.

The city is ruled under a "one country, two systems" deal, enshrined in the handover agreement, which allows it rights unseen on the mainland, including freedom of speech and an independent judiciary.

But there are concerns that China is increasingly interfering in a range of areas, from politics to education and the media.

Protesters at the bauhinia statue chanted "Long live the Umbrella Movement!" and "I'm a Hong Konger!"

The Umbrella Movement was the name given to mass rallies in 2014 calling for democratic reforms. Wong and Law were among the student leaders of those protests, which ultimately failed to win concessions.

Activists on Wednesday also called for the release of Chinese dissident Liu Xiaobo who was granted medical parole this week due to late-stage liver cancer but remains in the mainland.

The writer and Nobel Peace Prize laureate, now 61, was sentenced to 11 years in prison in 2009 for "subversion" after spearheading a bold petition for democratic reforms.

The bauhinia statue stands outside the convention centre where Xi will attend anniversary events and is a stone's throw from the hotel he will stay in.

The spot is popular with mainland visitors.

Some of the demonstrators, including Wong, had already draped the statue with a black flag on Monday during an early morning anti-China protest. It was removed by police.