HONG KONG, Oct 25 (AFP) - Amnesty International said on Monday (Oct 25) that it will shutter its offices in Hong Kong because of the threat posed to staff by a national security law that has fronted a sweeping crackdown on dissent in the business hub.

China imposed the law last year in response to massive and often violent protests, transforming Hong Kong's political, cultural and legal landscape and introducing mainland-style speech curbs.

Anjhula Mya Singh Bais, chair of Amnesty's board, said that the decision to close had been made "with a heavy heart" and was "driven by Hong Kong's national security law".

"(It) has made it effectively impossible for human rights organisations in Hong Kong to work freely and without fear of serious reprisals from the government," she added.

The decision ends more than four decades of the international human rights group's presence in the city.

Amnesty maintains two offices in Hong Kong.

The first is a local branch that focuses on human rights and campaigns in the city itself. Recent reports published by the team have included investigations into how the security law has been deployed and studies of the police's use of force against protesters.

The second office is a regional headquarters that carries out research and advocacy work across East and Southeast Asia and the Pacific.

Amnesty said that the local office would close on Oct 31 while the regional office would move out "by the end of 2021".

Hong Kong dubs itself "Asia's World City" and has long advertised itself as a business-friendly gateway to mainland China with its own separate legal system and speech freedoms unseen on the mainland.

As a result, many international businesses, media groups and non-governmental organisations have used the city as a regional hub.