A Japanese Air Self-Defense Force plane flying over southwestern Japan lost its cockpit canopy weighing dozens of kilograms.
The Defense Ministry says it has so far received no reports of injury or structural damage.
The ministry says an F-2 fighter jet's cockpit canopy separated from the aircraft on Sunday afternoon as it flew over mountainous areas of Asakura City, Fukuoka Prefecture.
The aluminum and acrylic glass canopy measures 150 centimeters long, 90 centimeters wide and 80 centimeters high, and weighs roughly 90 kilograms.
The ministry says SDF personnel have been dispatched to search for the canopy.
The fighter was scrambling in response to a possible violation of Japan's airspace.
But the mishap forced the plane to return to its base in the prefecture. The ministry said another fighter took its place to respond.
The ministry apologized for causing anguish to residents living near the base, and in areas where the canopy is believed to have fallen. It pledged to inspect all ASDF planes for possible abnormalities.