Ammunition box smashes through elementary school roof after falling from military helicopter

Base commander apologises as probe launched into how case fell from sky

The box fell from a US Army helicopter operating at Fort Bliss (Getty)

Authorities are trying to determine how a box of ammunition fell from a military helicopter before crashing through the roof of a school.

Ysleta Independent School District says no one was injured when the cache slammed into a building at Parkland Elementary School in El Paso, Texas, on Thursday afternoon.

The box punctured a hole in the roof upon impact and caused a power outage in part of the building, officials said.

The school stands meters from the perimeter of United States Army base Fort Bliss, home to the 1st Armored Division.

Colonel Jay Hopkins, commander of the division’s aviation brigade, apologised for the incident.

“I'm extremely sorry for any damage done to the neighbouring elementary school, and I am grateful that no one was injured,” he said.

“The incident is under investigation.”

Officials at Fort Bliss say they will now reassess flight patterns as part of the investigation into how the ammo box fell from the helicopter.

In December last year, the US Marine Corps sparked fury in Japan when a window fell off one of its helicopters mid-flight, falling onto a school playing field and injuring a child on the island of Okinawa.

The boy was lucky to escape the incident with only a minor arm injury after being hit by the window, which weighed around 20 pounds (9 kilograms).

“This is a regrettable incident and we apologise for any anxiety it has caused the community,” the US forces in Japan said in a statement issued at the time of the accident.

Additional reporting by AP