Three United States Marines have been killed and several more injured after their aircraft crashed off the Northern Territory coast during a training drill.

The Boeing MV-22B Osprey tilt-rotor aircraft was carrying 23 American personnel when it crashed during a routine training exercise about 9.30am on Sunday, the US military said.

“Three have been confirmed deceased while five others were transported to Royal Darwin Hospital in serious condition,” Marine Rotation Force – Darwin said in a statement on Sunday.

“The marines aboard the aircraft were flying in support of Exercise Predators Run.”

Recovery efforts were ongoing on Sunday night as investigation was launched into the cause of the incident.

Royal Darwin Hospital declared a Code Brown – the highest emergency response that can be activated at an Australian hospital – as it prepared to receive more injured marines.

NT Police Commissioner Michael Murphy said an emergency operation centre set up to tackle fires in the territory was redeployed to the crash site, with more injured to be transported.

“We are working closely with the Australian Defence Force, the US Marine Corps and other agencies such as Careflight to rescue and return those injured personnel to Darwin,” he told reporters on Sunday.

The national critical care and trauma response team was deployed and was triaging patients at crash site before they were transported.

“We are doing everything we can to return them safely back to Darwin for treatment,” Mr Murphy said.

He said the Tiwi Islands area where the crash occurred was remote, making moving the injured to hospitals difficult.

NT Chief Minister Natasha Fyles said the immediate focus was on transporting the injured to hospital for treatment.

“We acknowledge that this is a terrible incident,” she said

“We’re using Careflight airframes, both fixed wing and rotary, to respond, to get those people to Darwin into the care that they need.”

Ms Fyles said three operating theatres and several wards had been cleared as the hospital prepared to receive the injured marines. 

Darwin’s private hospitals were also on alert.

“Some people are critically injured, and so we’re focused on making sure that they get that level of care that they need,” Ms Fyles said.

“That is our ultimate priority right now is getting people across from the island to Darwin to receive that care.”

She said the site on Melville Island, about 80km from the mainland, had been secured and she had assured the US consul the NT’s resources were fully focused on the response.

The Department of Defence said the incident occurred during Exercise Predator’s Run 2023.

“Initial reports suggest the incident involves United States defence personnel and that Australian Defence Force members were not involved,” a Defence spokesperson said.

“At this critical early stage, our focus is on the incident response and ensuring the safety of those involved.”

Prime Minister Anthony Albanese, speaking in Karratha, said the ADF was working with its US partners to offer any assistance needed.

“Our focus as a government and defence department is on incident response and support at this difficult time,” he said.

“We are focused on providing practical assistance on the ground. 

“Obviously this is a regrettable incident.”

Mr Murphy said the Osprey that crashed was one of two that had flown from Darwin to Melville on Sunday.

About 150 US marines are stationed in Darwin and taking part in military drills alongside personnel from Australia and the Philippines.

Four Australian personnel were killed in an army MRH-90 Taipan helicopter crash off the coast of north Queensland in July.

The helicopter’s crew had been taking part in a multi-nation military exercise that also involved the US military.

By Kathryn Magann and Suzanne Simonot in Sydney