Authorities believed that a lightning strike during a severe storm triggered an electric detonator as the group was transporting explosives, the report from a local military newspaper said.

The explosion occurred on Monday night at a military shooting range of the 7th Military Region in Dong Nai, an industrial hub in southern Vietnam.

Authorities were still searching for several bodies of the victims, according to the report in the 7th Military Newspaper.

Fatal accidents during military training are rare in the communist country.

The accident came a day after Defence Minister Phan Van Giang delivered a speech to mark the start of the combat exercise, according to state newspaper Nhan Dan.

The ministry of defence has ordered an urgent investigation into the incident, the official Vietnam News Agency said.