Beijing has about 33,000 registered drug users and more than half use synthetic drugs, the capital's police authority said on Tuesday.

"The average annual increase of registered drug users in Beijing in the past five years was 12.3 percent with a growing number of synthetic drug users a major contributor to the increase," said Tao Jing, deputy head of Beijing Municipal Public Security Bureau.

Among registered users, about 22,000 use synthetic drugs while the rest use opiates.

According to the bureau, 62 percent of new drug users recorded last year were under 35. The youngest drug user was 12 years old.

Beijing police seized 280 kilograms of illegal drugs last year, nearly double the previous year's haul of 150 kilos. The number of suspected drug dealers detained in the city last year reached 11,000, more than three times the previous year's number. Of those, 660 suspects were involved in online trading of 56 kilos of illicit drugs.