Concern is growing in Hong Kong over the apparent disappearance of what is now five people linked to the same bookstore.
The booksellers specialised in publications critical of the Communist Party government.
Brianna Roberts reports.
The wife of 65-year-old Lee Bo, also known as Paul Lee, says he vanished after going to collect books from his warehouse in the city.
She says her husband later called her from a mainland Chinese number to tell her he was safe, but would not reveal his location.
She added he spoke to her in Mandarin even though the couple usually spoke Cantonese.
Mr Lee is a major shareholder of Causeway Bay Books, and his suspected disappearance is the fifth such case related to the bookstore in the past two months.
It is believed the publishing company behind the bookstore was about to launch a book about the former love life of President Xi Jinping.
Small groups of protesters have marched through central Hong Kong demanding to know what happened to the men.
Protest co-organiser Avery Ng says the fact the Chinese government would neither confirm nor deny its involvement in the disappearances has created widespread fear.
"The most scary thing is that there's no news and no proof of what happened to those five publishers. And even the central government and the Hong Kong government refused to respond -- well, previously -- on the whereabouts of these citizens are. Now if they did not make any arrest, then they (can) just come out and say it. But the fact is the Hong Kong police and the Chinese police did not respond to those questions. That creates the fears among the Hong Kong citizens."
Under Hong Kong's constitution, the semi-autonomous city enjoys the rule of law and freedom of expression.
The disappearances have added to unease that its freedoms are being eroded.
Hong Kong activists have staged protests outside the Chinese government's representative office in Hong Kong, demanding to know where the five booksellers are.
Among the activists is a retired political science professor at the City University of Hong Kong, Joseph Cheng, who says it is a concerning development.
"If this incident is proven true, then this certainly will be a rather alarming signal, and this will certainly generate an even stronger sense of self-censorship on the part of the journalist community in Hong Kong."
Another protester, Jeremy Tam, says it could undermine Hong Kong's basic law.
"It's terrible news, I have to say. When we first heard it, it was just absolutely terrible. I mean, under Hong Kong law, or 'One Country, Two Systems,' how could it possibly happen?"
Mr Lee's four colleagues at Mighty Current publishing company had gone missing from southern China and from Thailand about two months ago.
Mr Lee had been speaking to the media about their disappearances on the condition his full name would not be revealed.
Meanwhile, a separate demonstration has been held in Hong Kong to protest at the appointment of a pro-government official to Hong Kong's main university.
Hong Kong leader C.Y. Leung has selected Arthur Li to chair Hong Kong University's governing council.
Protester Ip Kin-Yuen says teachers and students view the appointment as a sign of growing political interference in Hong Kong's education system.
"The government's trying to get rid of some persons in the university, and now it is imposing some other persons into the university. I think it is quite clear that the government is very keen to make sure that the university is not opposing the government."
