Hundreds of police blocked roads and set up metal barricades around the China liaison office, angering protesters who pushed towards the front gates.
Police in Hong Kong skirmished with supporters of detained Chinese artist Ai Weiwei on Sunday in one of a series of protests planned around the world to demand Beijing free the prominent artist and rights campaigner.
Around 150 protesters, including seasoned pro-democracy activists and members of the former British colony's artistic community, held banners and carried a large democracy goddess statue demanding the release of Ai, 53.
"Return Weiwei to us," activist Lui Yuk-lin yelled, while members of the Hong Kong arts community, many dressed in black, carried photographs and wore badges of Ai bearing the word "Missing".
Hundreds of police blocked roads and set up metal barricades around the China liaison office, angering protesters who pushed towards the front gates, sparking tussles and the detention of at least one demonstrator.
The Hong Kong demonstration was part of a string of protests planned outside Chinese diplomatic compounds in major cities across Europe, the US and Australia, with supporters being mobilised on social networking sites including Facebook, which is banned in China.
Chinese media reports and the foreign ministry have said that Ai is being investigated for suspected "economic crimes," which they have not specified.
On Thursday, a Hong Kong newspaper under Beijing control said Chinese police have firm evidence that Ai had avoided tax.
China has arrested, detained or put in secretive custody scores of dissidents, rights lawyers, activists and grassroots agitators arrested since February, when fear of contagion from Middle East uprisings against authoritarian governments triggered a crackdown by China's domestic security apparatus.
"If we don't voice out, this could foreshadow what is to come," said Kacey Wong, a local artist and one of the demonstrators.
Ai Weiwei had a hand in designing the Bird's Nest stadium for the 2008 Beijing Olympics and has juggled an international art career with campaigns against government censorship and political restrictions, often using the Internet.
Ai has not contacted his family now for two weeks, since he disappeared into police custody at Beijing's international airport. His family says they have not been officially told anything by police, and they say the investigation into economic crimes is an attempt to silence Ai's outspoken activism.
"We still don't have any information about his situation, nothing," Ai's sister, Gao Ge, told Reuters on Sunday.
"Now as well, a lawyer who'd given him and us advice, Liu Xiaoyuan, is missing too."
Liu Xiaoyuan, has been unreachable since Thursday, adding to fears he may be the latest lawyer to have been detained. His mobile phone remained off on Sunday.
On Friday, Ai's wife, Lu Qing, and 14 other family members and colleagues of Ai and others who are missing issued a public letter to the ministry of public security and the Beijing Public Security Bureau demanding information about their whereabouts.
"We're expressing our fears about the situation of Ai Weiwei and other kidnapped and missing colleagues and friends.
Kidnapping citizens and forcible disappearance are serious criminal acts, and this has caused immense harm and dread for them and their friends and families," said the letter.
Ai's sister, Gao Ge, said the family had received no response to the letter, which was also put on the Internet.
In Beijing, police also sought for a second week to prevent members of a church that had been evicted from its former rented place of worship from attempting to worship outdoors.
The Shouwang congregation is one of the biggest Protestant "house" churches in Beijing that refuses to come under Party oversight, and it had urged members to gather for the outdoor service after they said official pressure forced the church out of a restaurant it had been renting for Sunday services.
The China Aid Association, a Texas-based group critical of Party controls on religion, said in an email that Beijing police had detained at least two Shouwang Church pastors and have "put all its lay leaders under house arrest."
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