Witness feared helicopter would crash into crowds after freak midair collision kills four

Witnesses say a horrific mid-air collision between two helicopters at Australia's Sea World theme park could have been far more lethal.

Four people were killed in the twin helicopter crash after the tail of a chopper taking off smashed into the cockpit of another coming in to land on the Gold Coast, the ABC reports.

The tail of the first helicopter broke off on impact, which hurled itself towards the ground.

The other aircraft crash-landed on a nearby sandbank, killing four on board.

Witnesses at the Gold Coast's Sea World theme park have since recounted hearing a deafening crash from above.

John Hunt told the ABC he feared one of the helicopters was going to crash on top of Christmas holiday crowds.

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"We looked up and we heard a bang and we saw one helicopter had hit and had already started to crash,'' he said.

"The other helicopter hovered over the Jelly Fish building [in the park]. We thought he was going to crash on top of all the crowd, but the pilot was able to get out onto the sandbank, probably an extra 30 metres away from where it was."

He praised the pilot who managed to land their helicopter on a nearby sandbank for saving lives as the theme park was 'choked with people'.

Mr Hunt added it was a 'pretty windy' day, but did not witness what had caused the crash.

Another witness, Steve Raschilla, told the ABC he saw one of the choppers 'break into pieces'.

"One of them from underneath, seemed like [it] came up and hit the bottom of the other one on top," he said.

"I don't know if they were both trying to land at the same time, [or] what they were trying to do."

Of the two helicopters, four people were killed and a further three from the crashed chopper were rushed to hospital in a critical condition.

Six people in the other helicopter that managed to land all survived.

Five patients in that aircraft suffered minor injuries and were taken to Gold Coast University Hospital for treatment, according to the Queensland Ambulance Service.

One person was physically uninjured.

Sea World Helicopters issued a statement expressing 'shock and deepest sympathy' for those involved in the freak crash.

"We are cooperating with all the authorities including the Australian Transport Safety Bureau and the Queensland Police. As it is now a police investigation we cannot provide any further information at this stage," the statement said, as per AAP.