From politicians to radio talk-back callers, most reacted with utter disbelief to news one of Australia's best-known icons had died.
Prime Minister John Howard said Irwin was a typical Australian larrikin who brought joy to millions of people around the world.
"I am quite shocked and distressed at Steve Irwin's sudden, untimely and freakish death," Mr Howard said.
"It's a huge loss to Australia. He was a wonderful character. He was a passionate environmentalist. He brought joy and entertainment and excitement to millions of people. He was a one-off character."
Queensland Premier Peter Beattie said a "great Australian" had been lost.
"It's a tragedy, it's shocked everybody," Mr Beattie said.
He said Irwin, who he met a number of times, had made a huge contribution to Queensland.
"He was a great Queenslander and a great Australian and he'll be sadly missed by everybody," he said.
Australian Tourism Export Council managing director Matthew Hingerty said the whole industry was in shock at the news.
"Not only was Steve Irwin a true Aussie icon, he was a fantastic ambassador for Australia and particularly for Queensland,” he said.
Foreign Minister Alexander Downer, who used a photograph of his family at Australia Zoo for his official Christmas card last year, hailed Mr Irwin for his work in promoting Australia.
Irwin was heavily involved in last year's "G'Day LA" campaign.
"The minister knew him, was fond of him and was very, very appreciative of all the work he'd done to promote Australia overseas," a spokesman said.
Mourners, including tourists and locals, have laid flowers at the entrance of Mr Irwin’s Australia Zoo on the Sunshine Coast.
Planet Ark founder Jon Dee said he was shocked to hear of the death of Mr Irwin, a Planet Ark ambassador whom he described as an "absolutely committed conservationist".
"One of the really sad things about today and what will become apparent is just how much money Steve put into wildlife conservation," he said.
He said he was very concerned for Mr Irwin's family, but also for the many wildlife charities and organisations he generously supported, or ran, such as his koala hospital.
Animal welfare organisation the RSPCA said Irwin was a modern day Noah because of his conservation work.
"His loss will be felt by animal lovers not just in Australia but all over the world," said RSPCA Qld chief executive Mark Townend.
"He was a modern-day Noah and should be acknowledged as such."
RSPCA Queensland spokesman Michael Beatty, who first worked with Steve Irwin when The Crocodile Hunter was just 15, said Mr Irwin's contribution to society would only truly be recognised in the years ahead.
"He put his money where his mouth was," Mr Beatty said. "Other people talked about it, Steve did it. His television series inspired millions of people all over the world to not only appreciate and understand wildlife, but to become active in the conservation movement."