BEIJING, Nov. 27 -- Chinese customs authorities have confiscated almost 20 tonnes of smuggled narcotics over the past decade, the general administration of customs (GAC) announced on Thursday.

The drugs, including heroin, methamphetamine, cocaine and opium, were seized in a total of 3,978 cases involving over 4,400 suspects, according to data released by the GAC.

Over 370 tonnes of raw materials for drug-making, such as ephedrine and acetic anhydride, were also seized.

Narcotics smuggling has soared in recent years. Customs authorities confiscated 5.1 tonnes of smuggled drugs last year alone, 11 times the total in 2005. Meanwhile, smuggling cases hit 466 last year, three times the number in 2005.

A global customs enforcement operation, codenamed "SKY-NET" organized by the World Customs Organization in close cooperation with the GAC in 2012, resulted in the discovery of 9.5 tonnes of illicit products.

The GAC said that the customs will maintain a rigid stance against drug smuggling as narcotics use is expanding. Customs authorities will also initiate a seven-month campaign on drug smuggling from December.

Drug use and drug crime is on the up in China. Public security assistant minister and drug control bureau chief Liu Yuejin said earlier this month that registered drug users numbered 2.76 million, but the actual number of users could be over 13 million.