A tourist snorkeling on Australia's Great Barrier Reef had his foot bitten off by a shark Tuesday before the predator turned around and mauled another person in his group, officials say.

The men were identified by Sky News as Alistair Raddon, 28, Danny Maggs, 22 from Britain. They told first responders that they were “wrestling and thrashing about in the water" during a snorkeling tour in the Whitsunday Islands when they were targeted.

The shark first severed one man's right foot and then circled back and mauled the other's right calf, according to Queensland state Ambulance Service spokeswoman Tracey Eastwick.

A rescue helicopter seen on its way to rescue two shark victims off the Australian coast. (RACQ CQ RESCUE)

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Both men were brought 7 miles by boat to the mainland town of Airlie Beach where paramedics were waiting for them, an ambulance official told the Associated Press. They were then flown by helicopter to a hospital in the city of Mackay, where they are reported to be in serious but stable condition.

ZigZag Whitsundays, the operators of the snorkeling tour the two men were on, told Sky News they are assisting authorities with the investigation.

"We have suspended our tours for today and will work closely with authorities regarding our upcoming tours,' the company said in a statement.

Shark attacks in the area -- an internationally renowned vacation destination -- are not uncommon.

A shark killed a 33-year-old man in November last year while he was paddleboarding in Whitsunday Island harbor.

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“They did everything imaginable to try to save the man. It’s just — the injuries were so severe,” Police Inspector Steve O’Connell said following that incident.

In September last year, two Australian tourists also were mauled on consecutive days, including a 12-year-old girl who lost a leg.

The Associated Press contributed to this report.