Two French tourists have died and another suffered a heart attack while snorkelling on the Great Barrier Reef off Cairns, Australia, today.

Authorities confirmed the visitors, all with pre-existing medical conditions, went into cardiac arrest while snorkelling in shallow water at Michaelmas Cay about 11am.

Two victims, identified as a 76-year-old man and a 74-year-old woman from France, were unable to be revived but the third was saved by trained staff onboard the Passions of Paradise vessel.

"It was a perfect storm of a fatal scenario with three French tourists suffering heart attacks at the same time," Association of Marine Park Tourism Operators chief Col McKenzie said.


"Crew on the Passions boat worked to save them all, including CPR and using oxygen, but tragically two are dead.

"There was a doctor onboard the nearby Ocean Spirit who declared them dead."

The third patient is being taken by boat to Cairns base hospital.

Passions of Paradise has extended its sympathy to the family and friends of the two elderly French travellers who died.

Chief Executive Officer Scotty Garden said the man and woman were among a French group of 21 elderly people on board the catamaran today.

"They had pre-existing medical conditions and were accompanied by a guide when they were in the water," he said.

"Passions of Paradise had a lookout on the beach, another on the boat and two snorkel guides in the water. All staff have current qualifications in CPR and first aid.

"The Passions of Paradise lookout on the beach noticed a man floating in the water and pulled him to the sand cay where he performed CPR.

"He was then assisted by a doctor on the sand cay.

"The Passions of Paradise lookout on the boat saw a woman floating in the water and pulled her on to the catamaran where CPR was performed.

"A third person later suffered a medical condition, but has survived."

Passions of Paradise has offered assistance to the group.

Michaelmas Cay is a popular tourist destination and is located about 40km northeast of Cairns.