Reports from the Quang Ninh Provincial Department of Labour, Invalids and Social Affairs said the accident happened at 3.30 pm on May 13 at the Quang Hanh-TKV Company. A landslide suddenly occurred and killed three male workers aged between 29 and 44. A 33-year-old worker was seriously injured and was sent to a local hospital.
Quang Ninh authorities are investigating the cause of the accident.
A methane gas fire last month at the Thong Nhat Coal Company in Quang Ninh killed four workers and injured seven others.
The state-owned Vietnam National Coal-Mineral Industries Group (TKV-Vinacomin) manages the Thong Nhat and Quang Hanh companies.
Deadly mining accidents are not uncommon in Vietnam. Last year, accidents claimed at least 10 workers' lives at the group's coal mines in Quang Ninh.