|Ai was placed under house arrest in November 2010 when the state also said it planned to demolish his studio [Reuters]
Supporters of the detained Chinese artist, Ai Weiwei, have scuffled with the police in Hong Kong, with at least one person being detained after protesters pushed through police barricades.
Around 150 protesters held banners and pictures of Ai on Sunday, and carried a large statue representing democracy.
Ai disappeared into police custody two weeks ago at Beijing's international airport. China's foreign ministry has said that the prominent artist was being investigated for unspecified "economic crimes".
Ai has juggled an international art career with campaigns against government censorship and political restrictions, often using the internet.
He also has a sense of humour: according to a profile of Ai in the New Yorker magazine, the artist is prone to calling the police and reporting the plainclothes state security agents who monitor his movements, describing the result as an "absurdist novel gone bad".
Ai's family says the arrest is an attempt to silence his outspoken activism.
A lawyer who had been advising Ai and his family has been unreachable since Thursday, prompting fears he may also have been detained.
The Hong Kong demonstrations were part of a series of protests planned outside Chinese diplomatic compounds around the world.
A small group of activists in Sydney, Australia, held a peaceful sit-in outside the Chinese consulates.
Similar demonstrations in London, Paris and Athens failed to draw more than a handful of protesters.