The illegal activity was discovered at the Dong An Vien Export-Import Company factory on August 6, Colonel Vu Van Hau, deputy director of the drug crimes investigation police department under Vietnam’s Ministry of Public Security, said at a press conference in Hanoi Tuesday. 

Two Vietnamese nationals were also arrested in the raid.

Hau said Vietnam has busted several drug manufacturing rings run by its citizens, but this was the first time the country has unearthed one run by foreigners.

The case was a result of collaborative efforts between Vietnam’s Ministry of Public Security, China’s Ministry of Public Security and other agencies, he added.

The factory is owned by a Vietnamese person in Kon Tum. The Chinese men had rented it to make illegal drugs. Hundreds of liters of drug precursors, 13 tons of chemicals, and 20 tons of machinery and equipment were seized.

The case will be investigated further by authorities in both countries.

At the conference, Hau also said that there had been an unusual spike in drug crime of late in Vietnam and the region. "Many foreign criminals are using Vietnamese territory to produce illegal drugs for domestic, regional and international consumption."

In the first nine months of this year, Vietnam dealt with 13,000 drug cases, arrested more than 20,000 people, and seized 750 kilograms of heroin, 571 kilograms of marijuana and 500,000 synthetic pills, the colonel said.

Vietnamese authorities deal with around 20,000 drug cases 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.

Vietnam is a key trafficking hub for narcotics from the Golden Triangle, an intersection of China, Laos, Thailand, and Myanmar that is the world's second largest drug producing area after the Golden Crescent in South Asia.