The regulatory stipulation that acts performed in the course of duty by the Office for Safeguarding National Security of the Central People's Government in the Hong Kong Special Administrative Region and its staff members shall not be subject to Hong Kong jurisdiction is reasonable and necessary and will ensure the office performs its duties in accordance with the law, Zhang Xiaoming, deputy director of the State Council's Hong Kong and Macao Affairs Office, said.

Addressing a news conference in Beijing on Wednesday on the Law of the People's Republic of China on Safeguarding National Security in the Hong Kong Special Administrative Region, which came into effect on Tuesday, Zhang said that because some of the cases handled by the office would involve State secrets, it was reasonable that the Hong Kong authorities could not have jurisdiction over the office and its staff members.

The central government has the power and responsibility to take all necessary measures to safeguard national security, he said.

Zhang said the office was an agency sent by the Central People's Government and was totally different from the agencies sent to Hong Kong by government departments, provinces, autonomous regions and municipalities. The power exercised by the office went far beyond the scope of Hong Kong's autonomy.

The law enforcement power of the office mainly concerned filing cases for investigation, taking necessary investigation measures, and arresting criminal suspects after submitting the case to prosecutors designated by the Supreme People's Procuratorate for approval, he said.

Given that the legal system in Hong Kong is different from that on the Chinese mainland, adopting two separated law enforcement and judicial bodies could avoid the conflict and confusion in the jurisdiction and application of the law, he said.

The law enforcement and judicial teams from the central government and Hong Kong will form a complete jurisdiction process, covering case filing, investigation, examination, prosecution, trial and penalty enforcement, forming a mechanism to safeguard national security in Hong Kong, Zhang added.

The national security law for Hong Kong includes a set of strict rules on the procedures of the office in the performance of its duties and their supervision, he said.

Article 55 of the law says the office will exercise jurisdiction over cases endangering national security only under three circumstances: if the case is complex due to the involvement of a foreign country or external elements, thus making it difficult for Hong Kong to exercise jurisdiction over the case; if a serious situation occurs where the Hong Kong Special Administrative Region government is unable to effectively enforce the law; or in circumstances involving a major, real threat to national security.

Shen Chunyao, director of the Legislative Affairs Commission of the Standing Committee of the National People's Congress, said the office will exercise its jurisdiction in strict accordance with the law.

"It shall, upon approval by the central government of a request made by the HKSAR government or by the office itself, exercise jurisdiction over a case concerning offenses that seriously jeopardize national security," he said.

"To tell the truth, we don't want to see the three circumstances take place — we don't want difficult situations or major practical threats to happen. But we must take such elements and risks into consideration when building a system.

"The move is made in line with the Chinese Constitution and the HKSAR Basic Law."