China's drug problem is severe and growing, the government said today, with particularly sharp rises in the abuse and production of synthetic drugs which have become a major health concern worldwide. Chinese seizures of methamphetamine, ketamine and other synthetic drugs surged by 106 percent year-on-year in 2016, said Liu Yuejin, vice director of the China National Narcotics Control Commission. At the same time the manufacture of drug precursors increased along with the production of New Psychoactive Substances (NPS), chemicals which mimic the effects of illegal drugs while exploiting loopholes in anti-drug laws. "Domestic production of crystalline methamphetamine, ketamine, and NPS was severe, not only consumed in the country but also smuggled overseas," Liu told a press conference, adding that the market for synthetic drugs keeps expanding and "in general, the drug problem is still spreading at a fast pace". Drug-producing areas had expanded considerably, he said. China is believed to be one of the main manufacturers of synthetic drugs - including opioids such as fentanyl - which have been blamed for public health crises in the US, Canada and Australia among other countries. The drugs are readily available for purchase online from manufacturers in China, who constantly tweak their formulas to keep the them one step ahead of laws that ban the products based on their chemical composition. Beijing has come under considerable pressure from abroad to curb the problem. Online sales of the drugs in China saw a sharp increase, said an annual report from Liu's commission released Monday, with contraband smuggled in postal parcels and other means. Two raids on online drug sellers last year ended in the arrests of 21,000 people, and the seizure of 10.8 tons of drugs and 52 tons of precursor chemicals, which can be used to manufacture synthetic drugs. Watch this also: [jwplayer o3Yxs7xZ] "Due to growing overseas demand, more precursors may be smuggled out of China," the report said. The use of synthetic drugs at home has also accelerated, it said, noting that drug usage in the country has undergone a "fundamental change" as users move away from opiates like heroin towards newly emerging drugs. In 2016 the number of known drug users in China rose 6.8 per cent to 2.505 million. Of these, more than 60 per cent consumed synthetic drugs (primarily methamphetamine and ketamine), 38 per cent used opiates such as heroin, and a little more than one percent cocaine and marijuana.