BEIJING, June 25 (Xinhua) -- Chinese customs throughout the country investigated 604 criminal cases relating to drug smuggling last year with 37.5 tonnes of various drugs and precursor chemicals seized, data from the top customs authority showed Tuesday.

Of the 604 cases, 596 were drug smuggling crimes and a total of 4.61 tonnes of drugs were seized, including heroin, cocaine, methamphetamine and cannabis, according to the General Administration of Customs (GAC).

A total of 400 drug smuggling suspects were arrested and 70 drug smuggling and trafficking gangs were busted, showed the data.

In the first five months of this year, nationwide customs investigated 284 drug smuggling cases and seized 567.35 kg of marijuana, heroin, codeine, methamphetamine and other drugs.

China will continue to maintain a tough stance against drug crimes, said a GAC official.