Dak Nong police arrested two men and uprooted thousands of cannabis plants, on Friday, at a coffee plantation in the Central Highlands.
Tran Xuan Luc, 42, and Nguyen Van Binh, 37, of Thuan Hanh Commune in Dak Song District were arrested at the site, Sai Gon Giai Phong reported Saturday.
Cultivating illicit plants is a crime punishable by up to three years in prison, under Vietnamese law.
Dak Song police said they raided the two men's 2.2 hectare coffee plantation and uprooted more than 2,000 cannabis plants that were growing among the men's coffee and corn.
All told, the seized marijuana crop weighed in at more than 5 tons.
They said that local residents had come to them and tipped them off that Luc and Binh were harvesting the illegal plants and carrying them out of the rural district in the middle of the night.
The residents said that the two farmers claimed that that they were cultivating medicinal herbs.
During the raid, police also seized a package of dried cannabis and more than VND100 million (US$4,860) in cash.
The arrestees confessed they had successfully harvested two crops and sold thousands of kilograms of cannabis, since early 2011, for nearly VND1 billion.
Police, who are investigating the case further, said it was the biggest marijuana seizure in the history of the province.