Corporal Spencer Collart, 21, Captain Eleanor LeBeau, 29, and Major Tobin Lewis, 37, were among 23 marines on board the Boeing MV-22B Osprey when it crashed on Melville Island, north of Darwin on Sunday morning during a military exercise for locally based troops.

Collart, from Virginia, was the Osprey's crew chief, LeBeau, from Illinois, was the aircraft's pilot, and Tobin, from Colorado, was the executive officer. All of them were stationed in Darwin.

Three other marines are still in Royal Darwin Hospital, one of them in critical condition, while the other 17 on board suffered minor injuries and have been discharged.

Colonel Brendan Sullivan, commanding officer of the Marines in Darwin, said the fallen trio had been "respected and beloved", adding: "Our thoughts and prayers remain with the families and with all involved.

"At present, we remain focused on required support to the ongoing recovery and investigative efforts."

Sullivan thanked the Australian Defence Force, local police and other emergency services workers who had "come together to assist us in this difficult time".

Authorities have not said what may have been the cause of the tragedy.

The investigation is expected to be lengthy, with officials spending at least 10 days at the crash site.