Around 30 cadets were injured last month during a pillow fight at a US military academy, according to reports.

The pillow fights at the United States Military Academy in West Point - which is located around 80 km north of New York City - are said to have been an annual tradition since at least 1897.

However things are believed to have gotten out of hand this year after some participants used pillows filled with hard objects.

The New York Times reports that there was at least one broken bone and a cadet knocked unconscious during the August 20th brawl, with at least 24 cadets suffering concussions. 

“West Point applauds the cadets’ desire to build esprit and regrets the injuries to our cadets,”Lt Col Christopher Kasker told the newspaper. “We are conducting appropriate investigations into the causes of the injuries".

The NY Times further reports that many cadets only spoke anonymously about the incident due to "West Point’s strictly controlled culture".

The pillow fight is intended as a 'harmless way of blowing off steam' after weeks of training, and the academy is said to have no plans to put an end to the tradition.

The academy is attended by around 4,000 cadets.