(CNN) -- Seven Marines were killed during a Marine Corps training exercise at Hawthorne Army Depot in western Nevada, the Marine Corps said Tuesday.
The cause of the incident is under investigation, the Marines said.
A representative of Nevada's Regional Emergency Medical Services Authority said four medical helicopters were sent to transport patients to regional hospitals.
Very little was immediately known about what caused the explosion.
Lt. Col. Craig Short, Hawthorne's deputy commander, said a traffic accident at the facility around 10 p.m. PT was related to the explosion, but he didn't explain what the connection was.
The Hawthorne Army Depot, about 140 miles southeast of Reno, is used for storing ammunition and weapon stocks awaiting demilitarization. The facility also provides high desert training facilities for military units.