Image copyright BBC Chinese Image caption The books the shop sells are banned in mainland China

Another associate of a Hong Kong bookshop specialising in titles critical of the Chinese government appears to have disappeared.

Last month four other employees of the same bookshop and publishing house, including its owner, went missing.

Their colleagues believe they have been detained because of their work.

Freedom of the press is guaranteed in Hong Kong, but many in the publishing industry say they are beginning to feel pressure from mainland China.

The latest associate to be reported missing is the man who raised the alarm when his colleagues disappeared in October.

Image copyright BBC Chinese Image caption The small shop is located in the busy Causeway Bay area

Mr Lee spoke to the BBC when his colleagues disappeared but did not want to disclose his full name at the time fearing reprisals.

He failed to arrive home on Wednesday evening and his wife has been unable to reach him. She told the BBC she is deeply afraid.

One of his colleagues said Mr Lee was taken away by unknown men and the fear is that Chinese officials have reached beyond mainland China to punish them for their work, our correspondent Juliana Liu in Hong Kong reports.

Two of the previous four men who disappeared were last seen in Shenzhen, mainland China, where their wives live; one was last seen in Hong Kong; and the other, the owner of the publishing house, was last heard from by email from Pattaya, Thailand, where he owns a holiday home.

The Causeway Bay Bookstore sells gossipy paperbacks that are highly critical of the Chinese leadership and are said to be popular among mainland tourists visiting Hong Kong.

The bookshop's troubles are not unique. Last year, Hong Kong publisher Yiu Mantin was sentenced to ten years in prison in China on smuggling charges his family believes were retaliation for publishing a book highly critical of President Xi Jinping. And in November, two Hong Kong journalists were tried for selling political magazines in nearby Shenzhen.