China's embassy in Wellington is accusing New Zealand of interfering in international relations with its decision to suspend extradition with Hong Kong.
Foreign Minister Winston Peters announced on Tuesday New Zealand was suspending its extradition treaty with Hong Kong after the passing of a controversial law.
China passed a national security law at the end of June which criminalises forms of political protest in Hong Kong with penalties including life imprisonment.
Peters said the legislation had "eroded rule-of-law principles" and undermined the 'one country, two systems' rule.
A spokesperson for China's embassy said the suspension was a "gross interference in China's internal affairs".
"The New Zealand Government's decision is a serious violation of international law and basic norms governing international relations. It is a gross interference in China's internal affairs. The Chinese side has lodged its grave concern and strong opposition," the embassy said in a statement.
"Hong Kong affairs are entirely China's internal affairs and allow no foreign interference.
"The Law on Safeguarding National Security in the Hong Kong SAR (Special Administrative Region) is an important step to ensure the steady and sustained implementation of the 'One Country, Two Systems' principle. Its implementation will strengthen Hong Kong's legal framework, ensure social order, improve business environment and contribute to Hong Kong's long-term prosperity and stability."