The stronger the bottom line of national security, the greater the room for "One Country, Two Systems," said Zhang Xiaoming, former director of the State Council's Hong Kong and Macao Affairs Office.

He made the remarks at a webinar to commemorate the 30th anniversary of the Promulgation of the Basic Law of Hong Kong on Monday.

Last month, China's top legislature adopted a decision to make a national security law for Hong Kong to counter foreign interference and attempts to seek independence for the special administrative region.

This is one of the most significant measures taken by the central government after Hong Kong's return to the motherland in 1997, a historical event during the practice of the "One Country, Two Systems," and a milestone in the implementation of the Basic Law, Zhang stressed.

"I have told many friends that without the enactment of the national security law on Hong Kong, the Basic Law cannot be fully implemented," he said.

Zhang explained why the legislation is necessary and urgent.

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Safeguarding China's sovereignty, security and development interests is not only inherent to the concept of "One Country, Two Systems," but also its core, the former deputy said.

"The central government's decision is based on the fact that the actions of hostile forces inside and outside Hong Kong have caused long-term chaos in the region and jeopardized national security," Zhang said, stressing that it is a must-do decision under the current political situation.

He also pointed out the legal basis for the legislation — national security affairs are affairs under the unified management of the central government, safeguarding national security legislation is the central government's responsibility, and any country will use all available measures to combat crimes that endanger its national security.

The legislation will only target acts of secession, subversion, terrorist activities as well as activities interfering with HKSAR's internal affairs by foreign or external forces, he highlighted.

Zhang also called for rational reflection on the legislation, saying that stigmatizing the central government and the SAR government's legal initiatives are common tricks played by the opposition and hostile forces.

"In my opinion, Hong Kong issues are not economic issues but political ones," he said, revealing that there are serious differences and even antagonism to the fundamental question of what kind of Hong Kong should be built.

"China has been firmly implementing the principles of 'One Country, Two Systems,' 'the people of Hong Kong governing Hong Kong' and a high degree of autonomy, while the external forces have tried to turn Hong Kong into a chess to contain China's development," he added.

HKSAR Chief Executive Carrie Lam also attended the meeting and reiterated the importance of understanding the initial purpose of "One Country, Two Systems" as well as the Basic Law.

"The proposal was put forward to safeguard the national sovereignty while ensuring the prosperity and stability of Hong Kong, so as to bring Hong Kong's greatest strengths into full play. The point has never changed," she stressed.