Speaking to reporters in Hong Kong Monday, Chief Executive Leung Chun-ying expressed concerns over the fate of Lee Bo — a Hong Kong bookseller who went missing several days ago and is believed to have been detained in mainland China. Lee, 65, is the fifth person associated with the Causeway Bay bookstore, which specializes in material critical of the Communist Party of China, to go missing in the past two months.

“The Hong Kong government is very concerned about the case,” Leung reportedly said, adding that the press conference was arranged as “it has been said that the incident may involve mainland legal enforcement agencies enforcing law in Hong Kong.”

“It would be unacceptable if mainland law enforcement agents enforce laws in Hong Kong because this violates the Basic Law,” Leung said, citing the “one country, two systems” policy that defines Hong Kong’s autonomy from China. “No other law enforcement agencies, outside of Hong Kong, have such authority.”

Lee, who is a shareholder of the bookstore popular among tourists from mainland China looking for reading material banned across the border, disappeared last Wednesday. The incident added to the growing unease in Hong Kong that the region’s autonomy was being slowly eroded, as Chinese authorities extend their crackdown on dissent.

Hong Kong (2) Messages of support are seen hanging on the door of a closed Hong Kong shop that sold books about China's politics Jan. 4, 2016. Photo: Getty Images/AFP/PHILIPPE LOPEZ

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However, there is “no indication” as of yet that Chinese authorities had any role to play in the disappearance of Lee or his colleagues, Leung said Monday. 

“If there is any indication that the missing person has surfaced at a location outside Hong Kong, the Hong Kong Police will take actions to verify that information,” John Lee, Hong Kong’s acting secretary for security, said in a statement Sunday, adding that Hong Kong police have asked China whether Lee is detained in the mainland and are awaiting a reply.

According to reports, the Mighty Current publishing house, which owns the bookstore, was planning to launch a book on the love life of Chinese President Xi Jinping.

“To my knowledge ... the book concerns the story about the girlfriend ... [from] some years ago,” Albert Ho, a Democratic Party legislator from Hong Kong, reportedly said Sunday. “There were warnings given to the owners not to publish this book. This book has not yet gone to print, but probably it [the disappearance] has something to do with this book.”