The Japanese government said Thursday it is "seriously concerned" about China's push, despite a growing international outcry, to impose a national security law that is feared will suppress political activity in Hong Kong.

Chief Cabinet Secretary Yoshihide Suga said a free and open Hong Kong should be maintained under the "one country, two systems" framework, and that Tokyo had relayed its view to Beijing before China's national legislature passed a resolution regarding the introduction of the law on Thursday.

"We are seriously concerned about the decision on Hong Kong by the National People's Congress despite strong concerns expressed by the international community and the people of Hong Kong, as well as about the current situation in Hong Kong," Suga, the top government spokesman, said at a news conference.