Of them, 11,800 or 50 percent are being treated at medical facilities and 1,200 are in detention centers while the remaining 10,500 are at large, Tran Ngoc Du, director of the Social Evils Prevention Division of the city's Department of Labor, Invalids and Social Affairs, said at a meeting on Monday.

Le Minh Tan, director of the department, said drug users are spread all over Saigon, the country's largest city with around 13 million people, including migrants.

While heroin has long been common among drug users in Vietnam, the use of synthetic drugs like meth and ecstasy has been rising of late, especially among partying youth.

Of the individuals registered for rehabilitation, 70 percent use meth, Tan said, as cited by Thanh Nien.

The media reports frequently about people publicly injecting themselves with drugs at bus stations, on streets, on and under bridges, and other locations.

Vo Van Trai, deputy head of the drug crime division at HCMC Police, said the actual number of people who use drugs is "many more and scary," referring to the widespread drug use that takes place in private places including bars and hotels.

The city has recently seized massive quantities of drugs, he said, mostly from foreigners who took advantage of the "flexibility" of the custom process.

In mid-May the city police seized half a ton of ketamine and arrested three Taiwanese and one Chinese.

This was just weeks after a haul of one ton of crystal meth.

Vietnamese authorities deal with around 20,000 cases involving drugs every year and arrest around 30,000 people. The country has some 250,000 registered addicts, but the actual figures are thought to be much higher.

The country developed its approach to drug addiction based on the presumption that it represents a "social evil" that can be cured with abstinence and re-education.

Following international criticism, the government established a timeframe in 2013 to gradually replace compulsory detention centers with community-based, voluntary treatment regimens.

The transition, however, has proven tricky given inconsistencies in the legal system, the widely-held belief that drug addiction stems from moral failure and the lack of competent doctors, therapists and equipment.