Steve Irwin, the man known around the world as the "Crocodile Hunter," has died in a stingray attack off the Great Barrier Reef.

Irwin, 44, had been filming a documentary off Port Douglas in northern Queensland when he was killed by a stingray barb through the heart. He was rushed to hospital by helicopter, but he died en route.

His documentary producer and longtime friend John Stainton was with him when he died.

"The world has lost a great wildlife icon, a passionate conservationist and one of the proudest dads on the planet," Stainton told the Australian Broadcasting Corp.

"He left this world in a peaceful and happy state of mind. He would have said, 'Crocs rule.'"

Irwin and a cameraman were snorkelling in shallow water when the intrepid animal-lover swam over the stingray, which then stuck out the barb, Stainton said, adding he believed his friend died instantly.

Irwin was famous for his enthusiasm for wildlife and his catchword "Crikey!" in his television program Crocodile Hunter. First broadcast in Australia in 1992, the program was picked up by the Discovery network, catapulting Irwin to international fame.

Carmel Robertson, with the Australian Broadcasting Corp., told CBC News that Australians are in shock.

"People can't believe that the man they thought was quite invincible is dead," she said.

Stingrays have a toxin-loaded spine on the top of their tail. Stings, while painful,are rarely fatal according to Shaun Collin,a University of Queensland marine scientist.

Collin said he suspected Irwin died because the barb pierced his heart.

"It was extraordinarily bad luck," Collin said.

Australian Prime Minister John Howard has expressed his condolences to Irwin's family, and said the country had lost a "wonderful and colourful son."

"He was the genuine article, what you saw was what you got: He took risks, he enjoyed life, but he brought immense joy to millions of people, particularly to children, and it's just such a terrible loss and I feel very distressed and I'm quite upset."

Queensland Premier Peter Beattie told ABC News online in Australia that officials were considering holding a state funeral for Irwin but were waiting to discuss arrangements with his family.

CNN reported on Monday evening that online tribute sites for Irwin were becoming overloaded and that many sites were crashing as people around the world tried to log on.

Irwin made news headlines in 2004 after involving his infant son in one of his crocodile stunts.

Irwin held his son Bob, who was a month old at the time, in one arm while he dangled a piece of chicken over the snapping jaws of a four-metre crocodile.

He later acknowledged that he should have done things differently and officials in Australia's Queensland state decided not to file charges against him.

Irwin's love for all things crawling began in 1970 when his reptile-loving father opened a small reptile park in Brisbane, Queensland.

In 1991, Irwin took over the family business and launched his Crocodile Hunter television program a year later.

Mourners have laid flowers at the entrance to Irwin's Australia Zoo.

"It was like hearing of the death of a really great friend," Lesley Manks told The Australian newspaper.

"It's hard ... it's hit home," said Manks, whoonce met the famous crocodile hunter.

Irwin is survived by his American-born wife Terri, their daughter Bindi Sue, 8, and son Bob.

The couple met when she went on vacation in Australia in 1991. She co-starred on her husband's television show and in his 2002 movie.