The national security law for Hong Kong will show "precious value" in the future, Zhang Xiaoming, deputy director of the State Council's Hong Kong and Macao Affairs Office, said on Wednesday, calling the law a "birthday gift" for the special administrative region as it marks the 23rd anniversary of its establishment.

The law is an important milestone in the cause of "one country, two systems", Zhang said at a news conference in Beijing after China's top legislative body unanimously passed the national security law for Hong Kong on Tuesday.

"The law is a turning point in Hong Kong's development to get back on track," he said.

The path of "one country, two systems" is unprecedented, so it is bound to be fraught with challenges in the course of pushing forward, and new problems constantly need to be solved, Zhang said.

The law, adopted by the Standing Committee of the National People's Congress on Tuesday, is the most significant step taken by the central government in handling Hong Kong affairs since the return of Hong Kong to the motherland, he said.

It is also the second major law specifically enacted by the central government for Hong Kong, following the special administrative region's Basic Law, he added.

Zhang said the Law of the People's Republic of China on Safeguarding National Security in the Hong Kong Special Administrative Region embodies the full implementation of the "one country, two systems" principle and further clarifies its bottom line.

By strengthening institutional barriers to prevent and control national security risks in Hong Kong, the law will have far-reaching impact on the stable and sustainable development of the cause of "one country, two systems", he said.

Zhang said the law is a new symbol of the central government's strategy to improve Hong Kong governance.

At the Fourth Plenary Session of the 19th Communist Party of China Central Committee, held last fall, the central leadership made major arrangements to improve the system of "one country, two systems" from the strategic perspective of modernizing the country's governance system and governance capacity, he said.

The implementation of the law indicated that the central government had paid more attention to the top-level design of the system of governing Hong Kong and the rule of law, and was targeting both symptoms and root causes of the issue with a combination of hard and soft measures, Zhang said.

The central government had used its powers under the Constitution and Hong Kong's Basic Law to firmly grasp the development direction and control the situation in Hong Kong, he added.

Zhang said the law will safeguard Hong Kong's prosperity and stability.

If various anti-China and anti-Hong Kong forces are allowed to stir up trouble in Hong Kong, or even turn Hong Kong into a base for infiltration and subversion against the Chinese mainland, it would be an absolute disaster for Hong Kong, he said. It would not only destroy the "one country, two systems" principle, but also destroy the prosperity and stability of Hong Kong and the well-being of its residents, he said.

This law aims to punish a small number of criminals who seriously endanger State security, deter external forces from interfering in Hong Kong affairs, and fully protect the lives and property of the vast majority of Hong Kong residents and their rights and freedoms. It also fully protects the legitimate rights and interests of foreign investors in Hong Kong, he added.

Zhang said that when he listened to views on the drafting of the law a week ago, businesspeople and professionals, as well as school principals and taxi drivers, all expressed sadness about the chaos and devastation that followed the violence that started in Hong Kong last June.

"They told me that some people in Hong Kong want to emigrate because they are afraid of the violence and because they can't see a way out," he said.

"Many people in Hong Kong have expressed the view that it is high time that Hong Kong turned from chaos to order. I think this law can have a transformative effect to stabilize Hong Kong.

"It is normal for some people to be skeptical or hesitant when this law first comes out. I firmly believe that time and facts will tell."