Two boys are fighting for their lives, and four others remain in hospital after the mid-air collision of two helicopters on the Gold Coast, killing four people.
One helicopter landed safely near the Sea World theme park, with a pilot, four New Zealanders and a Western Australian on board.
The other crashed, killing the pilot, a British couple and another adult.
Australian correspondent Murray Olds says there are numerous lines of inquiry.
He says it appears mechanical failure has been ruled out, but there are questions around whether the pilot's view was impaired by a passenger or was fatigue a factor.
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