A shock helicopter crash on Australia's Gold Coast has killed four people and injured more than a dozen

The collision between the two choppers sent one aircraft hurtling upside down into a sandbar on Main Beach, outside Sea World.

Three passengers - a woman and two young boys - are in a critical condition at Gold Coast University Hospital.

Acting Inspector Gary Worrell says the cause is still unclear, but it appears one helicopter was taking off and the other was landing.

He says one helicopter was able to land safely on the beach, although it's windscreen was blown out - injuring those inside.