For the second time in less than a week, an object from a Marine Corps aircraft has reportedly landed on school grounds in Okinawa, Japan.

At 10:09 a.m. on Wednesday, a window from a CH-53E Super Stallion fell onto a sports field of an elementary school outside Marine Corps Air Station Futenma, Marine Corps officials announced.

About 50 children were outside on the school grounds at the time, and one 10-year-old boy was slightly injured “by the wind pressure” caused from the falling object, the Yomiuri Shimbun reported on Wednesday.

Corps officials declined to confirm whether a student had been injured.

“We take this report extremely seriously and are investigating the cause of this incident in close coordination with local authorities,” III Marine Expeditionary Force said in a statement.

Separately, media outlets have reported that a small, cylindrical object fell from another CH-53E onto the roof of a Japanese nursery school on Dec. 7. The Marine Corps said it is investigating the incident, but has not yet announced whether the object came from a Marine aircraft.

Meanwhile, an Air Force F-35A lost a panel over the Pacific Ocean about 65 miles east of Okinawa during a Nov. 30 training flight. The 18th Wing did not announce that the incident until Dec. 4.