Two workers in Tien Giang Province died after inhaling methane from a biogas trench at a breeding farm Sunday.
Four of them were pumping waste from the trench in Nguyen Thi Thanh's farm when the accident happened.
One of them climbed down into the trench to investigate a problem, but did not return. The others went down to check what had happened.
Two of them, 24 and 27 years old, died on the spot while the others, 25 and 57, were saved at the Tien Giang General Hospital later that night.
One of the men who died, Duong Thanh Luan, managed to pull his colleague to safety, said local residents who had rushed to help the workers.