The chief editor of a Hong Kong publishing house who has been critical of the Chinese government has become the fifth member of staff to have gone missing from the firm since October.
Hong Kong police confirmed Lee Bo's "missing person" status, which follows a spate of disappearances among staff at Mighty Current publishing house, known for producing controversial books about mainland Chinese politicians.
Last seen in Hong Kong at the publishers' warehouse on Wednesday (30th December), Lee Bo, 65, was reported missing by his wife on Friday (1st January), the Guardian reported.
Lee's wife Sophie Choi told the paper that she had started looking for Lee when he didn't come home Wednesday night around 7pm. Choi received a call from Lee at 10pm "to tell me everything all right" but not from a number she recognised and originating from a Chinese city, Shenzen, in Guangdong Province.
The BBC said Lee "is thought to be in detention in mainland China".
Owner Gui Minhai, along with general manager Lui Bo, store manager Lam Wing-kei and staff member Cheung Jiping were reported missing between 22nd and 24th October 2015.
There is speculation that an upcoming book from the firm, about a mistress or girlfriend of the Chinese President Xi Jinping, may have prompted the "detentions".
At the time of his colleagues' disappearances in Autumn, Lee had said: “I think [it has happened] probably because of publishing matters... political books banned on the mainland.”
Fears as to the whereabouts of owner Gui, a China-born Swedish national, emerged after he went missing while on a trip to Thailand to visit his holiday home. His last communication was an email informing his printers to a new book he would be sending over the proofs for shortly, but never did.
Hong Kong's chief secretary, Carrie Lam, issued a statement on Saturday (2nd January) that she was concerned about reports that the bookseller had gone missing, while Hong Kong acting secretary for security John Lee said police were “actively” investigating the case.
A demonstration was held outside Beijing's representative office in Hong Kong yesterday (3rd January) to protest the latest disappearance of Lee.
Protester Raphael Wong told the BBC: "Freedom of [a] person is inviolable. If the central government arrest a Hong Kong resident and [take them] back to mainland China, this is a threat to our freedom of press and also freedom of speech."
The International Publishers Association has also expressed "serious concerns" for the publishers.
IPA president Richard Charkin said: "We are seriously concerned for these people's safety. If they have indeed been arrested, then this is another example of the Chinese government's campaign to try to silence dissent in Hong Kong. The IPA calls on the Chinese government to immediately declare whether these four people are indeed being detained and if so, on what charges. In any event, we ask the Chinese government to do everything in its power to assist in locating the publishers and allowing for their safe return."
The president of PEN International, Jennifer Clement, added: "PEN International is deeply concerned by the recent reports of four missing publishers in China. If it's confirmed that they are in detention, it will be yet another blow to the declining situation for freedom of expression in the country. Chinese authorities should investigate these reported disappearances and immediately clarify the situation."