Kadena Air Base, the largest U.S. Air Force installation in Japan, experienced a sudden explosion on Monday morning at an ammunition storage site in southern Okinawa.

According to Japan’s Ministry of Defense, the blast occurred at a temporary facility used to store unexploded ordnance. Four individuals were injured, though no serious injuries have been reported so far.

Local media outlets, including Jiji Press and NHK, stated that the cause of the explosion remains unclear as investigations continue to determine the reason and assess the damage.

Yuta Matsuda, a local official in the nearby town of Yomitan, commented, “We received reports of an explosion at a Self-Defense Forces facility, and there are reports of injuries, but we don’t have further details at this point.”

Kadena Air Base is of significant strategic importance to the U.S. military presence in the Pacific region, located just about 370 miles from Taiwan.