Two Malaysian military helicopters collided and crashed during a training session on Tuesday, killing all 10 people on board, the navy said.

The helicopters were rehearsing at a naval base in northern Perak state for the navy’s 90th anniversary celebration next month when the accident occurred, the navy said in a brief statement.

“All victims were confirmed dead on site,” it said, adding that the remains have been sent to the hospital to be identified.

A video circulating on social media showed several helicopters flying low in a formation. One of the aircraft veered sideways and clipped the rotor of another helicopter, causing both to plunge and crash.

A local police officer confirmed that the video footage was genuine.

The helicopters were mangled beyond recognition. Rescue workers sifted through the debris to find the bodies. The victims included three women and seven men, police said.

Prime Minister Anwar Ibrahim said the nation mourned over the “heart and soul-wrenching tragedy” and that the navy would immediately carry out an investigation to determine what had caused the accident.

Seven crew members were aboard the AW139 maritime operation helicopter, the navy said.

That aircraft is produced by AgustaWestland, which is a subsidiary of the Italian defence contractor Leonardo.

Three other crew members were on a Fennec lightweight helicopter, manufactured by European multinational defence conglomerate Airbus.

Local media reported that the AW139 crashed at a sports complex at the naval base, while the Fennec hit a nearby swimming pool.

The navy said it will launch an investigation to determine what caused the accident.