Two helicopters collided mid-air on Monday, killing four and seriously injuring three in Australia's Gold Coast tourist region, authorities said.

Television images showed the rotors of a device lying on a sandbar a few meters from the shore of the Gold Coast (Gold Coast) in the south-east of the Australian region of Queensland.

Nearby, one of the two helicopters was overturned on the sand near the shore, according to the public broadcaster ABC.

The other aircraft appeared largely intact at the crash site, which is near the Sea World marine theme park.

The two aircraft “on colliding, crashed [...] into the sandbar just outside Sea World Park,” Queensland Police Inspector Gary Worrell said.

"As a result, four people lost their lives today" and "three others are in critical condition in hospital," he added during a press briefing on the spot.

After the crash, a bright yellow rescue helicopter touched down on the sand as dozens of rescuers spread out across the field, TV footage shows.

Several police and rescue vessels stood ready to intervene near the sandbar strewn with debris from the two helicopters.

The Australian Transport Safety Board announced the opening of an investigation into the accident, presented as a "mid-air collision".

Investigators were expected on site to examine the wreckage, map the site and recover investigative material, the office said in a statement.