JOHANNESBURG (AP) — An apparent gas leak at a naval base in the South African city of Durban killed six people Friday, including three members of the military, authorities said.

The men were "overcome by gas" while working in a sewage pit, said Russel Meiring, a spokesman for paramedic company ER24.

In a statement, ER24 described the incident as a "freak accident."

Three members of the military and three civilian employees of the public works department died from the gas at Natal Naval Station, according to the South African defense ministry. Several other people were injured.

Authorities were investigating.