A missing bookseller in Hong Kong said via fax on Monday that he went to the Chinese mainland "by his own  means" and has been assisting an investigation, Taiwan's Central News Agency (CNA) reported.

An employee surnamed Chen at Causeway Bay Books bookstore was quoted by CNA as saying that Lee Bo, a major shareholder in the bookstore, faxed a letter to him explaining that he was dealing with emergencies and  managed to go to the Chinese mainland "by his own means" to assist an investigation into an unnamed party.

Lee, who was reported missing on December 30, also said that the investigation may last for a while and assured Chen that he is fine.

Lee's wife withdrew the report of his disappearance at a local police station on Monday afternoon, Hong Kong-based TVB News reported.

She claimed that she managed to get in touch with her husband "via other people," according to TVB News. However, the police have not confirmed the information.

After Lee's disappearance, his wife was quoted by Hong Kong media as saying that she received calls from Lee in which he said that he was assisting an investigation. She said the phone numbers indicated that the calls were made from Shenzhen in South China's Guangdong Province.

The Public Security Bureau in Shenzhen told the Global Times on Monday that they "have no knowledge of the case."

The Hong Kong Immigration Department also has no record of Lee's leaving Hong Kong.

Lee's disappearance followed those of four other people in Hong Kong's publishing circle. Among those missing is China-born Swedish national Gui Minhai, who worked for publishing house Mighty Current, which also runs the Causeway Bay bookstore.

Some bookstores in Hong Kong also sell books about rumors surrounding senior political figures, making use of a special legal framework that differs from that on the Chinese mainland.

Hong Kong's Chief Executive Leung Chun-ying said at a news conference on Monday that any efforts by law enforcement agencies from outside to enforce laws in Hong Kong would go against the Basic Law and the "one country, two systems" policy.

He added that the Hong Kong government is highly concerned about the disappearance of those people, calling for citizens to  provide any relevant information to Hong Kong authorities.