Two Helicopters crash near Australian Sea World theme park killing four

Two helicopters collided on the Australian Gold Coast, killing several passengers and critically injuring three others.

One helicopter appeared to have been taking off and the other landing when they collided near the Sea World theme park at Main Beach, a northern beach on the Gold Coast.

One helicopter landed safely on a sandbank, but debris from the other was spread across an area police described as difficult to access.

The dead and three most seriously injured people were all passengers in the crashed helicopter.

"Members of the public and police tried to remove the people and they commenced first aid and tried to get those people to safety from an airframe that was upside down," said Gary Worrell, Queensland state police acting inspector.

"(People on) Jet skis, family boaters, ordinary members of the public rushed to assist these people."

Passengers in the other helicopter, which lost its windscreen in the crash, are also receiving medical assistance.

Footage of the crash showed a helicopter shortly after take-off being clipped by another aircraft flying over the water.

Sea World Helicopters, a separate company from the theme park, expressed its condolences and said it was co-operating with the authorities handling the crash investigation.

It did not confirm if it operated one or both helicopters involved in the crash, saying it would not comment further because of the investigation.

A witness named John told Melbourne radio station 3AW that patrons at Sea World heard the crash, and staff moved swiftly to close off areas closest to the crash.

"There was a massive, massive bang," he said. "It was just huge. I'm not sure if it was the propellers or whatever hitting against each other. But there was this poor lady and her son near the helipad in tears."

Queensland premier Annastacia Palaszczuk said the accident was an "unthinkable tragedy".

"My deepest sympathies are with each of the families and everyone affected by this terrible accident," she said.

Australian Transport Safety Bureau chief commissioner Angus Mitchell said an investigation into the cause of the crash was under way.

The Gold Coast region is at its busiest in January, the peak time for holidays in Australia's summer.