Police officers check the site where five workers were killed at Foodtech JSC in Hoa Hiep Industrial Zone in Phu Yen Province on January 12

According to deputy director of Phu Yen Province's Department of Public Security, Nguyen Trung Nghia, the accident occurred at 11am at Foodtech JSC in Hoa Hiep Industrial Zone in Dong Hoa District.

"The victims, including a Thai national, are all men aged from 22-50," Nghia said. "We have transferred the bodies to Phu Yen General Hospital for investigation.

Director of Phu Yen Economic Zone Management Board, Le Van Thanh cited a report from Hoa Hiep Industrial Zone as saying that the workers choked to death after they inhaled a toxic gas in the fish-sauce basin.

"Initial report said that a worker came down to check the basin and did not return. Then other people also died when coming down to find him," Thanh said. "We are carrying out further investigations into the case."

Thai-invested Foodtech JSC specialises in processing fish products and has operated in Hiep Hoa Industrial Zone for many years.