Two British nationals, believed to be a husband and wife, were among four people killed when two helicopters collided midair near Australia’s Gold Coast on Monday, police said Tuesday.

Investigators believe one helicopter was taking off while the other was landing, authorities said Monday. One crashed on a sand bank near the shore, with photos showing the aircraft upside down, while the other helicopter was able to land safely.

All deceased and seriously injured victims were in the helicopter that crashed. Six people in the other helicopter suffered only minor injuries.

The pilot and three passengers, ages 36 to 65, died at the scene, according to Queensland state police.

A 10-year-old boy was critically injured, and remains in critical condition. Also seriously injured was a 9-year-old boy now in stable condition, and a woman, 33, in critical but stable condition, police said.

The collision took place near the popular tourist strip of Main Beach on the Gold Coast, opposite the Sea World resort.

One helicopter had been a few hundred meters in the air, though the exact altitude of the collision has yet to be determined, said Australian Transport Safety Bureau (ATSB) Chief Commissioner Angus Mitchell on Tuesday.

“We’re still determining the exact sequence of events, but from the footage that we’ve seen and the damage that we witness, it does appear that the main rotor blade of the helicopter taking off has collided with the front cockpit of the descending helicopter on the left-hand side,” he said. “Now, exactly if that was the very first point of impact, we’re yet to determine.”

The helicopter taking off had been airborne for fewer than 20 seconds before the collision – and hit the ground in a matter of seconds, he added.

Mitchell said investigators are working to salvage the wreckage and will be interviewing witnesses and survivors over the next few days.

The investigation will look at a range of influences, including the weather, how long the helicopters had been operating, how long the pilots had been flying and what was happening in the cabins, Mitchell said.

In a message on its website, Sea World Helicopters said it was “devastated by the tragic accident.”

“Our deepest sympathy and condolences go out to all those involved over this very sad time. We are closed until further notice and will refund all tickets purchased,” the statement said.

The Village Roadshow Theme Parks (VRTP), a division of Village Roadshow Limited which operates theme parks and attractions in Australia and the United States, offered its condolences in a statement on the Gold Coast Sea World Facebook account.

It added that it was working with emergency services and providing support to its team members. “As it is now a police investigation, we cannot provide any further information at this stage,” the statement said.

Australian Prime Minister Anthony Albanese tweeted his “deepest sympathies” to those affected. “Australia is shocked by the news of the terrible and tragic helicopter incident today on the Gold Coast,” he said Monday. (CNN)

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