CANBERRA, Australia -- Two elderly French tourists died of heart attacks moments apart while snorkeling on Australia’s Great Barrier Reef on Wednesday, officials said.

The 76-year-old man and 74-year-old woman died while diving with a group of 21 elderly French people at Michaelmas Cay, north of Cairns in Queensland state, said Association of Marine Park Tourism Operators executive director Col McKenzie.

“It just appears to be the perfect storm: two events occurring at the same time,” McKenzie told The Associated Press.

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“We’re dumbfounded. In 35 years, I’ve never seen a similar event,” he added.

The benign weather and sea conditions could not explain the tragedies, McKenzie said.

The group had been diving from a catamaran operated by Cairns-based Passions of Paradise when the tragedy occurred late morning, he said.

Both victims had declared “pre-existing medical conditions” in paper work before they went into the water, said the company’s chief executive, Scotty Garden.

Two guides went into the water with the group, while lookouts were posted on the catamaran and the sand.

The lookout on the beach first noticed the man floating motionless and pulled him to the sand, where the staff member performed cardiopulmonary resuscitation, Garden said.

Moments later, the lookout on the catamaran saw the women floating face down. She was taken to the catamaran, where attempts were made to resuscitate her, Garden said.

Staff used bottled oxygen and defibrillation equipment without success. A doctor from another tourist boat also assisted efforts and declared both snorkelers dead, McKenzie said.

A third French diver was later initially suspected to have also had a heart attack. But the man was later thought to have had an anxiety attack and recovered, McKenzie said.

“He watched two of his travel companions in massive trouble. It would give anybody heart palpitations,” McKenzie said.

Passions of Paradise is an award-winning operation that has taken more than 400,000 tourists to the reef since 1989, according to McKenzie. The company’s only previous fatality was an 80-year-old who died from a heart condition in 1997, he said.

Police are preparing a report for a state coroner, who will determine the official causes of the deaths.