"The two helicopters collided during flight training. All 10 victims on board have been confirmed dead by the medical officers," Suhaimy Mohamad Suhail, senior operations commander from the fire and rescue department said.

Footage shared online showed several helicopters flying low in a formation over the Lumut naval stadium in a flypast rehearsal ahead of the navy fleet's open day celebrations in May.

One of the choppers was seen clipping the rear rotor of another helicopter, causing both to go into a tailspin and crash.

The two helicopters involved were a Eurocopter AS555SN Fennec and an AgustaWestland AW139, the rescue agency said.

Photos showed the Eurocopter model heavily mangled in the wreckage on the naval base stadium track with rescue personnel surrounding it as well as various debris.

The AgustaWestland helicopter crashed at the naval base's swimming pool area.

Prime Minister Anwar Ibrahim sent his condolences to the families of the victims, saying "the nation mourns the heart-wrenching and soul-wrenching tragedy".

"I was informed that an immediate investigation will be carried out by the Ministry of Defense, especially TLDM (Royal Malaysian Navy), to find the cause of the crash," he said.

Incidents involving helicopters are not uncommon in the Southeast Asian nation.

Last month, a Malaysian coast guard helicopter crashed in the Strait of Malacca with no fatalities.

In 2016, a deputy minister was among those who died after a Eurocopter AS350 crashed in the Malaysian state of Sarawak.