A window fell out of a United States helicopter and landed in a school sports ground in southern Japan in an incident likely to fuel tensions between military and residents.

Around 50 children were on the grounds of the elementary school near Futenma marine airbase in Okinawa when the window fell from a US military transport helicopter.

One boy reportedly sustained minor injuries from the fallen window, photographs of which appeared in local newspapers lying on the ground with a metal and yellow frame.

Okinawa, the southernmost region of Japan, hosts the majority of the 38,000 US troop stationed in the country, with the region widely viewed as a strategic launchpad for American military activity across Asia.

The US Marines in Okinawa issued a statement apologising for the mishap: “We take this report extremely seriously and are investigating the cause of this incident in close coordination with local authorities. This is a regrettable incident and we apologize for any anxiety it has caused the community.”