China agreed Monday to talks with Hong Kong in the wake of explosive revelations by a city bookseller who said he was detained for eight months on the mainland, as fears grow that Beijing is tightening its grip.

Lam Wing-kee was one of five employees of a Hong Kong firm -- which published gossipy books about leading Chinese politicians -- to go mysteriously missing last year. All later emerged in mainland China.

Lam, 61, has said he was seized after crossing the border into the southern Chinese city of Shenzhen, taken away blindfolded and then kept in a cell, under interrogation and without access to his family or a lawyer, for alleged involvement in bringing banned books into the mainland.

Hong Kong's Beijing-backed chief executive Leung Chun-ying, who has been accused of dragging his feet over the case, said last week he had written to Beijing relaying local concerns, amid growing anxiety that the semi-autonomous city's freedoms are disappearing.

In a short statement Monday, Leung said he had received a reply from Beijing "to start discussion on the existing notification mechanism between the two places".

Under that system, authorities on the mainland are required to give clear details about arrests and detentions of Hong Kong citizens over the border, a procedure critics say went disastrously wrong in the booksellers' case.

Beijing's public security ministry confirmed the discussions should take place as soon as possible.

"The existing notification mechanism has been in operation for more than a decade and it is necessary to be improved," the ministry said in a statement, inviting the Hong Kong government to send a delegation to Beijing.

During the talks, authorities in the mainland would also brief Hong Kong about Lam's case, the statement said.

Leung expressed gratitude for what he described as a "positive response".

He said last week that he had asked Beijing to clarify how relevant mainland departments handle cases in which Hong Kong people have broken mainland laws, and whether or not mainland personnel had carried out cross-border law enforcement in the city.

In the case of bookseller Lee Bo, the only one of the five to disappear on Hong Kong soil, China was accused of illegally sending its security agents to operate in Hong Kong.

Lam reported to Hong Kong police Monday to tell them formally about his detention and said he would be returning for further discussions.

"The police will review Lam's testimony and decide if they will investigate," said pro-democracy lawmaker James To, who accompanied Lam.

Hong Kong was returned by Britain to China in 1997 under a deal which allows it freedoms unseen on the mainland, but there is concern they are now being eroded.