Another missing Hong Kong bookseller has returned to Hong Kong, and asked local authorities to drop his missing person case, police said.

Lee Po is one of five men linked to book publisher Mighty Current and the Causeway Bay bookstore who went missing at the end of last year. They later turned up in mainland China, claiming to be assisting authorities with an investigation of their colleague Gui Minhai.

“Lee Po told police that to assist in an investigation of a case relating to a person surnamed Gui, he, with the assistance of his friends, returned to the mainland by his own means voluntarily and it was not an abduction,” a police statement said.

Lee’s disappearance sparked concerns that Chinese authorities had forcibly taken him from Hong Kong without the knowledge of local police, in violation of local laws and a treaty with Britain that keeps Hong Kong’s legal and governance system separate to that of mainland China until 2047.

The British Foreign Office said in February that Lee was likely to have been “involuntarily removed” to China. Beijing denied it.

Three other men linked to Mighty Current - Lui Por, Cheung Chi-ping and Lam Wing-kee - admitted to Phoenix TV earlier this year that they along with Gui had sold thousands of books illegally on mainland China.

They have all been arrested and charged. Lee is the only one that has not been charged by Chinese authorities.

Causeway Bay Books was known for selling works containing rumours about high-ranking members of the Chinese Communist Party.

- dpa