The four victims were transferred to hospital for treatment after the incident, where three later died.
Vu Doan Quang, director of the Hai Duong provincial Department of Labour, Invalids and Social Affairs, said on May 8 that the Department had dispatched an investigation group to the scene and will report their findings to the Ministry of Labour, Invalids and Social Affairs.
The cause of the incident is still under investigation, said Mr Quang.
A representative of Hoa Phat Steel JSC said the company initially offered VND30 million to the family of each fatality, and sent staff to provide care for the injured person as they recover in hospital. All of the costs of treatment will be covered by the company.