Australia's internationally renowned "Crocodile Hunter," Steve Irwin was killed Monday by a stingray barb to the heart as he was filming underwater.

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Irwin, 44, was struck in shallow waters as he was filming a documentary on the Great Barrier Reef called "Ocean's Deadliest", The Australian reported. His crew pulled him aboard his research vessel, Croc One, summoned a rescue helicopter and sped to a meeting point 30 minutes away as they performed CPR on him, reports said.

Australian Prime Minister John Howard said he was "shocked and distressed by Steve Irwin's sudden, untimely and freakish death," the BBC reported.

"It's a huge loss to Australia, he was a wonderful character, he was a passionate environmentalist, he brought entertainment and excitement to millions of people," Howard said.

The Melbourne-born naturalist's "Crocodile Hunter" program was first broadcast in Australia in 1992 and is shown around the world on the Discovery cable network. Irwin also starred in movies and helped develop the Australia Zoo wildlife park, north of Brisbane, which was started by his parents Bob and Lyn Irwin.

Irwin is survived by his U.S.-born wife, Terri, daughter Bindi, 8, and three-year-old son Bob.