Washington (AFP) - Thirty cadets who just completed their first-year summer training at the prestigious US Military Academy at West Point were injured when an annual pillow fight tradition turned bloody, The New York Times reported.

The brawl left 24 young cadets with concussions, The Academy told the paper, after reports that some stuffed their pillows with hard objects.

A total of 30 cadets were injured, and students reported that the list of wounds included one broken leg as well as dislocated shoulders.

The yearly right of passage is meant to foster class spirit and celebrate the first-year "plebe" class's completion of its rigorous summer training.

However, the August 20 pillow fight took a turn for the worse when some cadets reportedly stuffed the helmets they were encouraged to wear during the fracas inside their pillow cases.

"Mitigating measures" had been put in place by the upperclassmen who oversaw the event, such as requiring cadets to wear helmets, academy spokesman Lieutenant Colonel Christopher Kasker said in the Times.

Video posted on YouTube showed several hundred students vigorously socking each other with pillows during the free-for-all in a courtyard. Pictures of bloodied cadets were also posted on Twitter.

"West Point applauds the cadets' desire to build esprit and regrets the injuries to our cadets," Kasker said. "We are conducting appropriate investigations into the causes of the injuries."

No disciplinary measures have been taken against the cadets and there were no plans to end the yearly brawl, the Times said.

Some cadets told the paper that one student who was knocked unconscious had not yet returned to class, however Kasker insisted all cadets were back on duty.

West Point has a long history of pillow fights, dating back to at least 1897, the Times added.

The military academy's 2013 fight was canceled after a cadet put a lockbox in a pillow case the previous year, it said.