The workers were cleaning mud out of a water collection tank at the Duyen Hai Thermal Power Company in Tra Vinh province on Thursday when they suddenly fainted, the Vnexpress news site reported.

They were pronounced dead after being taken to a local hospital.

An initial investigation suggested the workers had suffocated following a gas leak at the plant's pumping station.

Due to poorly enforced safety regulations, Vietnam has a high rate of workplace deaths.

In 2017, 928 people were killed at work.

By Bac Pham - Deutsche Presse Agentur - December 28, 2018