Beijing police have detained almost 11,000 criminals engaged in drug-related activities, seizing 71.7 kilograms of drugs since 2016，the capital's police authority said on Thursday.

"The average annual increase of registered drug users in Beijing in the past 10 years was 15.6 percent," said Tao Jing, deputy head of Beijing Municipal Public Security Bureau, adding that 700 of those detained were under the age of 18.

He said the number of registered drug users in the capital reached 36,000 in 2016, increasing 7.3 percent year-on-year from 2015. Since 2008, 4,800 drug-related criminal cases occurred around the Fifth Ring Road and in areas even further from downtown.

Online instant messaging platforms, including WeChat and QQ, have been major channels for drug users to get drugs, said Tao.

He said many of the seized drugs in the past 10 years in Beijing come from overseas. While 59 percent, or 200 kilograms, of the seized heroin was from the Golden Crescent (Afghanistan, Iran and Pakistan), more than 97 percent, or 80 kilos, of the seized cocaine was from South America.