Alistair Raddon, 28, had his right foot bitten off in the attack, while 22-year-old Danny Maggs suffered serious lacerations to his right calf.
The pair were on a day cruise and snorkelling near Hook Passage, a body of water between Whitsunday Island and Hook Island which is a popular tourist destination.
Paramedic Billy Ludvigsson, who was also on the cruise, said: “Back at home when I work in the ambulance we have time to prepare for the assignment, this time we didn’t.
“We had to make a makeshift tourniquet with ropes and towels to stop the bleeding.
“It was severe, life threatening at first.
“But we managed to stop the bleeding pretty fast, actually, in a couple of minutes, maybe five minutes.”
Emma Andersson, an emergency room nurse, said: “We didn’t have time to prepare.
“We started with the man who was worse first. The other man’s leg didn’t look so bad.
“The other man had lost his foot and we decided to work more with that, to stop his bleeding first.”
Mr Ludvigsson added: “I think that saved his life, because he was bleeding so badly.
“It was a long boat ride back to shore and if he continued to bleed that much all the way back to shore I’m not sure he would have made it.”
A statement on Wednesday from the base hospital in Mackay, 600 miles north of Brisbane, said both men were in a stable condition.
There have been a number of shark attacks in the Whitsunday islands in recent years, including a fatal incident at Cid Harbour involving a 33-year-old man last November.
Australia has averaged fewer than two deadly shark attacks per year in recent decades.
According to Australian Shark Attack File and excluding Tuesday’s incident, there have been 10 injuries from unprovoked shark attacks this year.
Reporting by PA.