Hong Kong's status as an international financial center will not be undermined by the sanctions imposed by the United States, and China has full confidence in the special administrative region's future, said Zhang Xiaoming, deputy director of the State Council's Hong Kong and Macao Affairs Office.

Fundamentally, Hong Kong's status as a global finance center and its long-term prosperity and stability depends on two factors —whether or not its advantages in the business environment and financial system will be affected, the other is whether or not the momentum of the mainland's economic development and the central government's support for the SAR will be weakened, he said.

"For these two factors, we have confidence. Therefore, we are very optimistic for Hong Kong's future," Zhang said at a press conference in Beijing on Wednesday.

The Standing Committee of the National People's Congress, China's top legislature, unanimously passed a national security law for Hong Kong on Tuesday, prohibiting acts of secession, subversion, terrorism and collusion with foreign or external forces that endanger national security.

The law was added to Annex III of the Basic Law and took effect later on Tuesday.

On Monday, the US announced sanctions on China for the implementation of the national security law, including revoking HKSAR's special trade status, halting defense exports and restricting its access to high-tech products.

In response, China also announced countermeasures, imposing visa restrictions on US citizens who have "behaved egregiously" over Hong Kong-related issues.

Zhang said the US moves only give an opportunity for China to demonstrate its determination and ability to defend itself and fight back.

"If the US takes measures, the Chinese government and the government of HKSAR will fight back. The countermeasures will come as the situation may call for," he said.