The bookshop known for its sensational titles on political intrigue in Beijing and whose managers have recently disappeared, sparking a public outcry over suspected China interference, was set to reopen on Monday (Feb 1) after being closed for more than a month, Hong Kong media reported.

The wife of Causeway Bay Books co-owner Lee Bo, who was last seen on Dec 30, told Radio Television Hong Kong on Saturday that the bookstore would reopen on Monday, but she did not say if or when Mr Lee would return to Hong Kong.

As of early afternoon Monday, the doors of the shop remained shut, South China Morning Post reported.

Mr Lee, who also co-owns the publishing house Mighty Current, disappeared in Hong Kong while four others, including his business partner Gui Minhai, disappeared while in Thailand and mainland China.

They are all believed to have been detained by the mainland authorities. Mr Lee has contacted his wife from the mainland, saying that he is assisting with an investigation.

The mainland authorities confirmed to Hong Kong that Mr Lee, 65, was "understood" to be on the mainland.

Chinese state television earlier this month broadcast a video of Mr Gui, a naturalised Swedish citizen, confessing to a mainland drink-driving offence that dates back a decade and saying he did not want Stockholm to interfere with his case.

On Sunday, Causeway Bay Book's gates were still shut and plastered with news clippings, pictures and messages of support, South China Morning Post said on Monday. A "Closed" sign remained scribbled with notes accumulated over the last five weeks including the words "Never rest" and "Not afraid".

Mr Lee's wife, Ms Sophie Choi, could not be reached for comment, the daily said.

There was no indication of when its doors would open on the shopfront or website, it added.