Irwin, 44, died this morning after being fatally injured while filming a nature documentary off Queensland.
The news has shocked the nation and prompted a rush of tributes from politicians and the public alike.
Irwin's wife Terri was in Tasmania at the time of the tragedy and had to be contacted by police with the terrible news.
Dr Ed O'Loughlin was aboard the Emergency Management Queensland Helicopter which was called from Cairns at 11.21am (AEST).
Irwin was being given CPR at Low Isles, off Port Douglas, as the helicopter arrived less than one hour after the incident, but Dr O'Loughlin said nothing could be done to save him.
"It became clear fairly soon that he had non-survivable injuries," Dr O'Loughlin said.
"He had a penetrating injury to the left front of his chest.
"He had lost his pulse and wasn't breathing."