Police confiscated 12.51 kg of drugs including methamphetamine and heroin last week in Guangzhou, capital of south China's Guangdong province, they said.
The arrests were made in a hotel and a rental house in the city's Yuexiu District on December 28 after police seized crystal meth from mail on December 26 and launched a probe.
The bureau did not disclose the nationalities of the suspects, the state-run Xinhua news agency reported.
Drug trafficking is a felony in China. Those convicted of trafficking more than 50 grammes of heroin can face capital punishment.
Police across China have cracked 56,000 drug cases and broken up 1,174 trafficking gangs, the Ministry of Public Security said in a statement.