Public security officials say vendor who disappeared in October, then was released in June, is overdue back on the mainland for further investigation
China has reportedly warned Hong Kong bookseller Lam Wing-kee that he could face harsher legal action for violating bail conditions.
A statement issued by the Ningbo Public Security Bureau said Lam had broken his bail terms by failing to return to the mainland for further investigation after his initial eight months in detention, Hong Kongs Ming Pao newspaper reported.
Lam was one of five booksellers whose disappearances over the past year have been linked to the Causeway Bay Books store that had specialised in publishing and selling books about Chinas leaders, including President Xi Jinping.
Lam was allowed to returned to Hong Kong in June. The Ningbo Public Security Bureau said unspecified criminal enforcement measures would be triggered by his failure to return to the mainland.
The South China Morning Post reported that Chinese authorities had released a video of Lam during his time in detention. In a video link on the newspapers website, Lam could be seen eating, being given a haircut and making comments.
On his return to Hong Kong last month Lam said Lee Bo, who went missing from Hong Kong in late December, had been abducted, and said cross-border enforcement actions by mainland Chinese authorities in Hong Kong were not acceptable.
Lam said he was arrested last October in the southern Chinese city of Shenzhen, then blindfolded and taken to the eastern city of Ningbo, where he was kept in a small room by himself and repeatedly interrogated about the selling of books banned on the mainland.
The disappearances have prompted fears that mainland Chinese authorities may be using tactics that erode the one country, two systems formula under which Hong Kong has been governed since its return to China from British rule in 1997.
Chinas public security minister, Guo Shengkun, met a Hong Kong delegation in Beijing on Tuesday to discuss the detainee notification system between the two police forces, which needs to be modified and improved, the ministry said.
The delegation was also briefed on Lams case, Xinhua news agency added, without elaborating.
Hong Kong enjoys far wider personal freedoms and protections than exist on the mainland. No formal extradition treaty exists between the two jurisdictions.
Lam pulled out of a protest march in Hong Kong on 1 July citing concerns for his personal safety after he noticed several people following him in recent days.
Hong Kong police said after meeting Lam on Monday that there was no evidence his personal safety was at risk. They advised him to call for police assistance if needed, a police statement said.