Three US marines are dead and 20 are injured, five seriously, after a US aircraft crashed on the Tiwi Islands near Darwin during a multinational military exercise, authorities have confirmed.

Marine Rotational Force Darwin, a United States Marine Corps Marine Air-Ground Task Force based in the NT said the incident happened at 9.30am on Sunday.

"There were a total of 23 personnel on board," it said, in a statement.

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"Three have been confirmed deceased while five others were transported to Royal Darwin Hospital in serious condition."

NT Chief Minister Natasha Fyles held an emergency cabinet meeting after the crash, which she described as a "terrible incident".

"Australia and the US are working together to respond to this incident," Fyles said.

NT Police Commissioner Michael Murphy said two Bell Boeing V-22 Osprey tiltrotor aircraft took off from Darwin heading to the Tiwi Islands on Sunday morning.

They were part of exercise Predators Run, which involves the militaries of the United States, Australia, Indonesia, the Philippines and East Timor, the Australian Defence Department said.

The islands are 80 kilometres from Darwin.

Reports came in that one of the aircraft had crashed two kilometres inland on Melville island, Murphy said.

An emergency operation centre monitoring bushfires was redirected to launch a rescue mission, with the ADF and CareFlight also involved.

"Those injured are 23 US marine corp soldiers and we are doing everything we can to return them safely back to Darwin for treatment," Murphy said.

"Five marines have been returned to Darwin for treatment with the remaining being triaged at the scene."

A code brown was declared at Darwin hospital to indicate the incident could impact the facility, Fyles said.

Australian Prime Minister Anthony Albanese described the crash as a "difficult inciden".

"Obviously this is a regrettable incident. I am unable to give further information at this time," Albanese said.

Since The Osprey started flying 33 years ago, 51 service members have been killed.

However it has a lower mishap rate compared to many other aircraft flown by the US military.

The Osprey is a tiltrotor aircraft. It takes off like a helicopter, then the engines tilt forward enabling it fly at much faster speeds than a helicopter.

The club is $2 million short of the $7.5m needed to rebuild the clubrooms.

Santamaria claimed he was “not aware of any power imbalance at the time”.

Police responded to the crash on State Highway 3 near Troopers Road, Te Mapara at 3.45pm.

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Two Australian tourists have been seriously injured in 10-metre fall from a medieval wall in Croatia.

A woman, 26, is fighting for life, according to local media, and a man, 34, is in a serious condition.

The couple fell from a wall between two restaurants in Dubrovnik, a popular holiday destination in the European country's south, in the early hours of Saturday morning local time.

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Local media reported the pair fell after leaning on the wall.

They lost their balance when the woman leant against the man.

The man has had surgery and the woman is in intensive care, according to reports.

Dr Ivan Benčić, a trauma specialist at Dubrovnik General Hospital's trauma unit, told Croatian media outlet HRT the woman had suffered cerebral damage and multiple fractures in her vertebrae in the fall.

"We are constantly monitoring her and doing everything we can to fight for her life," he said.

Andrijana Biskup, a spokeswoman for Dubrovnik-Neretva police told Dubrovacka Televizija that the couple had been cuddling or kissing when the fall happened and said alcohol may have played a part, according to the Sydney Morning Herald.

She said the man had a blood alcohol reading of just over 0.2, and the woman's was 0.3.

DFAT confirmed it is providing consular assistance to two Australians injured in Croatia.

The city, which is famous for being used as a location for TV show Game of Thrones, attracts millions of visitors a year.

Parts of the walls date back to the 13th century.

The design allows for contractors to be safely separated from traffic.

“Little to be positive about” in the Govt’s terms a week ago, according to deputy mayor.

‘I think it is bullying and harassment. What else would you call it?’

One person is being taken to the hospital with critical injuries.