They are not police station. They are undercover agents, who can be prosecuted as unregistered agents of a foreign power (and if they are diplomats can be expelled for engaging in inappropriate activities).
China has not had a “communist” economic system for over a generation. It has system of “free” enterprise with heavy involvement by the government in guiding the economy. Its political system, while showing some traces of its “communist” origin, is basically a standard authoritarian dictatorship. In most ways, China more closely resembles Germany during the Third Reich, or Italy during the fascist period, than a “communist” country such as China during Mao’s leadership, or the Soviet Union.