Hong Kong police offered protection on Wednesday to a bookseller who was detained in China for eight months without access to a lawyer, as Beijing warned that he was violating his bail terms.

Lam Wing-kee was seized after crossing the border into China and taken away blindfolded for allegedly bringing banned books into the mainland, he said last month.

The 61-year-old is part of a group of staff from a Hong Kong firm that published salacious titles about leading Chinese politicians.

The five mysteriously went missing late last year and later emerged in mainland China, intensifying concerns in Hong Kong about China's increasingly tight grasp on the city.

Since returning to Hong Kong, Lam has said he fears for his personal safety while other activists have alleged that Chinese agents abducted one of the other booksellers on Hong Kong soil.

Although the city has the status of a special administrative region of China, the two have separate legal systems, distinct police jurisdictions and maintain strict border controls.

The city was returned by Britain to China in 1997 under a deal guaranteeing freedoms that would be unimaginable in the mainland, and the case has fanned anxieties that the semi-autonomous city's fiercely guarded liberties are being eroded.

Lam is the only one of the five booksellers to speak openly about the case and has suggested the other four feel too much pressure from China to do the same.

He was supposed to return to the mainland after being released to Hong Kong on bail last month but has refused to do so.

The case has put the city's China-friendly Chief Executive Leung Chun-ying in a very awkward position, trapped between his political masters in Beijing and Hongkongers angry about the city's direction.

- Forced confession -

"The government and I are paying close attention to the issue of Lam Wing-kee's concerns for his personal safety," Leung told reporters Wednesday.

Hong Kong and China have no extradition treaty, meaning there is no obligation for city authorities to hand Lam back to China even if he is violating the terms of his bail.

Police deputy commissioner Tony Wong said officers were willing to offer Lam protection "if he wishes it".

Activists have alleged that Chinese security agents are operating in the city, which would be illegal under the city's mini-constitution.

Lam had been due to lead a pro-democracy march last week on the anniversary of the city's handover from Britain to China, but pulled out at the last minute, saying that he had been followed prior to the rally.

The police comments came after a new video released by Chinese authorities featured him in detention saying: "I am very regretful because I have broken Chinese laws".

Lam has previously said he was forced into making the confession.

Chinese authorities have warned Lam he was violating his bail terms and that he could face tougher action as a result, media reports said.

Leung said a team of senior officials who visited Beijing Tuesday discussed Lam's case and reviewed the mechanism whereby authorities on the mainland are required to give details about arrests of Hong Kong citizens over the border.

Leung said the visit was productive, with both sides agreeing that mainland authorities should notify their Hong Kong counterparts of arrests and detentions within 14 days.