Authorities in Vietnam arrested two Taiwanese and a Chinese national on Saturday who were allegedly linked to a seizure of 500 kilograms of synthetic drugs.

The police and customs departments coordinated with the drug crime investigation department under the Ministry of Public Security during the operation that took place on May 11, VN Express reported. Chinese national Su Jia Mei, 33, and Taiwanese nationals Jhu Munh Jyun, 32, and Liu Ming Yang, 34, were arrested.

Jhu’s 36-year-old Vietnamese-Taiwanese girlfriend Nguyen Thi Thu Van was also detained during operations that saw warehouses in Binh Chanh, Tan Binh and Tan Phu districts raided. A total of 500 kilograms of ketamine was found concealed in four packaging printers in a seven-seater vehicle.

According to police, the haul was worth more than 500 billion dong (US$21.42 million,) making it the largest amount of ketamine ever confiscated in the country. Liu was thought to be the leader of the drug ring.

On March 14, Jhu received four packaging printers from China at the border in Quang Ninh province as instructed by Liu. Jhu then took them to Binh Chanh district, where the group was set to move the drugs to a third market when the bust took place.

Top police officers in the country have pointed out that the favorable logistics infrastructure in Ho Chi Minh City has made it a hub for drug trafficking.