A big task ahead for officials to piece together what caused a mid-air collision between two helicopters on the Gold Coast, which claimed four lives.

One helicopter landed safely near the Sea World theme park on Monday, with a pilot, four New Zealanders and a Western Australian on board. The other crashed, killing the pilot, a British couple and another adult.

Aviation Commentator Peter Clark says something has happened which has distracted the pilots, but the cause is unknown.

He's led to believe these machines may not have voice recorders, so investigators have a lot of work to do.

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