A senior Hong Kong delegation will head to Beijing for talks following explosive revelations by a bookseller who said he was detained for eight months on the mainland, the city's leader said Monday.

Lam Wing-kee, 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 without access to a lawyer for alleged involvement in bringing banned books into the mainland.

The case has laid bare growing anxiety that the semi-autonomous city's freedoms are disappearing.

Lam 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.

Hong Kong's Beijing-backed chief executive Leung Chun-ying said a team of senior officials would visit Beijing Tuesday to discuss Lam's case and review the "existing notification mechanism between the two places".

Under that mechanism, 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.

"(Officials) will go to Beijing tomorrow morning ... (and) meet with relevant departments in order to improve the existing mechanism. It will be a comprehensive and in-depth review," Leung told reporters.

He added mainland authorities would also brief the Hong Kong officials, including the city's justice and security ministers as well as heads of police and immigration, on Lam's case.

Lam was due to lead a pro-democracy march Friday to mark the 19th anniversary of the city's handover from Britain to China, but pulled out at the last minute citing a "serious threat" to his security.

Hong Kong security minister Lai Tung-kwok said Lam had filed a report over his claims and investigation was underway.

The Hong Kong government has been accused of dragging its feet over the booksellers' case, with residents demanding to know what authorities have done to try to help them. There have also been accusations China has illegally sent its security agents to operate in Hong Kong.

Fellow bookseller Lee Bo disappeared on Hong Kong soil, spurring fears that he was detained by Chinese personnel.

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.