TOKYO, June 4 (Xinhua) -- A thin rubber sheet about the size of a hand dropped onto a school in Japan's Okinawa on Tuesday, local media reported, and the Okinawa Defense Agency was checking whether the object was from a U.S. military aircraft.

According to local media, an object fell from the sky onto the tennis court of a junior high school in the city of Urasoe in Okinawa Prefecture, at about 3:30 p.m. local time.

More than 20 students were at the tennis court practicing club activities when the incident happened. The object fell close to the students, but caused no injury. Meanwhile, students said they saw a helicopter flying near the scene.

The object was about 18 cm high, 12 cm wide and weighs about 20 gram with the shape like a thin rubber sheet.

The Okinawa Defense Agency was checking whether the helicopter was a U.S. military aircraft and whether it was linked to the falling object.

The junior high school is located about 1 km west of the Nishihara Interchange on the Okinawa Expressway, and there are also elementary schools and nursery schools around the area.