BRISBANE, Australia — A helicopter carrying American tourists crashed at a coral-viewing site on Australia’s Great Barrier Reef, killing two and injuring two others, police said.

The helicopter pilot pulled one passenger from the wreckage after the crash Wednesday but desperate attempts to revive the 65-year-old woman failed, Police Inspector Ian Haughton said Thursday. A 79-year-old man also died despite bystanders’ attempts to resuscitate him, Haughton said.

A 34-year-old man and a 33-year-old woman were taken to the Australian mainland for treatment of non-life threatening injuries, he said.

All four tourists knew each other.

The crash occurred 40 miles northeast of the Whitsunday Islands on a pontoon that has underwater viewing chambers to see coral and is a popular tourist destination.

Whitsunday Air Services suspended operations as it works with authorities to determine the cause of the crash. “We are extremely saddened by this incident and our deepest condolences are with the families of all of the passengers,” the company said in a statement.

The Australian Transport Safety Bureau confirmed a crash investigation was underway.