Dinh Hat, 32, died on the way to a hospital from serious bites in the incident Monday in Son Linh village in Quang Ngai province, said village official Nguyen Tuyen. Quang Ngai is about 900 kilometers (560 miles) south of Hanoi.
The other two farmers were hospitalized, with one of them in serious but stable condition Wednesday, he said.
The farmers were working on their cassava fields when they saw a wild boar, Tuyen said. They cornered the animal with machetes, intending to kill it for meat, but were attacked instead, he said.
Tuyen said other villagers later killed the boar.