legal ground
Article 2 of the Frontier Health and Quarantine Law of People's Republic of China (PRC).
People's Republic of China (PRC) shall, in accordance with the provisions of this Law, set up frontier health and quarantine offices for ports, airports, land borders and river ports (hereinafter referred to as frontier ports) that are open to international navigation, and carry out quarantine, monitoring and health supervision of infectious diseases.
Article 16 of the Frontier Health and Quarantine Law of People's Republic of China (PRC).
Frontier health and quarantine offices have the right to require entry and exit personnel to fill out health declaration cards and produce vaccination certificates, health certificates or other relevant documents for certain infectious diseases.