CANBERRA, Australia (AP) — Eight U.S. Marines remained in a hospital in the Australian north coast city of Darwin on Monday after they were injured in a fiery crash of a tiltrotor aircraft that killed three of their colleagues on an island.

All 20 survivors were flown from Melville Island 80 kilometers (50 miles) south to Darwin within hours of the Marine V-22 Osprey crashing at 9:30 a.m. Sunday during a multinational training exercise, Northern Territory Chief Minister Natasha Fyles said.

All were taken to the Royal Darwin Hospital, and 12 had been discharged by Monday, she said.

The first five Marines to arrive at the city’s main hospital were critically injured and one underwent emergency surgery.

Fyles said she would not detail the conditions of eight who remained in the hospital out of respect for them and their families.

“It’s ... a credit to everyone involved that we were able to get 20 patients from an extremely remote location on an island into our tertiary hospital within a matter of hours,” Fyles told reporters.

The Osprey that crashed was one of two that flew from Darwin to Melville on Sunday as part of Exercise Predators Run, which involves the militaries of the United States, Australia, Indonesia, the Philippines and East Timor.

All 23 Marines aboard the lost aircraft were temporarily based in Darwin as part of the Marine Corps’ annual troop rotation.

Around 150 U.S. Marines are currently based in Darwin and up to 2,500 rotate through the city every year. They are part of a realignment of U.S. forces in the Asia-Pacific that is broadly meant to face an increasingly assertive China.

The bodies of the dead Marines remained at the crash site, where an exclusion zone would be maintained, Northern Territory Police Commissioner Michael Murphy said.

The cause of the crash had yet to be explained and investigators would remain at the site for at least 10 days, Murphy said.

The Osprey, a hybrid aircraft that takes off and lands like a helicopter, but during flight can tilt its propellers forward and cruise much faster like an airplane, crashed into tropical forest and burst into flame.

Emergency responders were surprised the death toll was not higher.

“For a chopper that crashes and catches fire, to have 20 Marines that are surviving, I think that’s an incredible outcome,” Murphy said.

“Our thoughts are with the three Marines that have died during service for their country, and our thoughts go out to their country, to the United States Marine Corps and all their colleagues and friends,” he added.

Defense Minister Richard Marles was also greatful that the toll was not worse.

“It’s remarkable that in many ways, so many have survived,” Marles told Nine News television.

“This remains a very tragic incident and the loss of those lives are keenly felt,” Marles added.

U.S. Defense Secretary Lloyd Austin paid tribute to dead Marines.

“These Marines served our country with courage and pride, and my thoughts and prayers are with their families today, with the other troops who were injured in the crash, and with the entire USMC family,” Austin tweeted.

The U.S. Embassy in Australia issued a statement offering condolences to the families and friends of the dead Marines and thanking Australian responders for their help.