Queensland Ambulance Service's (QAS) Tracey Eastwick said it was believed the pair, who had been day tripping on a vessel, were mauled while snorkelling in Hook Passage.
"One of the male patients was attacked first and the shark is believed to have returned and attacked the second patient," Ms Eastwick said
The CQ Rescue Helicopter Service said Alistair Raddon, 28, told members of their crew he and 22-year-old Danny Maggs had been wrestling and thrashing about in the water when the attack occurred.
Tracey Eastwick from QAS said the pair were given first aid by paramedics from overseas who happened to be on the boat.
"They've applied tourniquet to both patients and continued treatment into Abell Point Marina where they've met two of our ambulance frontline crews there," Ms Eastwick said.
Paramedic Steve Thurtell said the men were in good spirits
The English tourists were conscious and alert while being flown from Airlie Beach to Mackay Base Hospital in a serious but stable condition.
Mr Raddon lost his foot in the attack while
Hook Passage is located between Hook Island and Whitsunday Island, around 25 kilometres from Airlie Beach.Mr Maggs suffered serious lacerations to his calf.
Tour company ZigZag Whitsundays said its thoughts were with the men and their families.
"We are working with authorities to assist in any way we can. We have suspended our tours for today and will work closely with authorities regarding our upcoming tours."
Whitsunday Mayor Andrew Willcox said about 20 people were on board the boat when the incident happened.
"It's a very quick boat so they came straight back in and the Ambulance Service was already on site," he said.
"As soon as the boat docked, the ambos went straight to work. I tell you what, I can't praise the Queensland Ambulance Service enough."
He said the tourists have been offered counselling.
Tourism Whitsundays chief executive Natassia Wheeler said tour companies take safety very seriously.
"Before anyone enters the water they do checks and they check around their surroundings as well. But like anywhere you travel in the world, when you're in the environment you must take caution of the environment you're in."
Ms Wheeler said she did not believe there had ever been drum lines in the area where the attack happened.