The victim suffered significant leg and torso injuries in the attack, which occurred near Lindeman Island.
The last shark attack in the area was eight years ago.
RACQ CQ Rescue Helicopter crewman Ben McCauley said the doctor and others who gave first aid to Ms Barwick before she was winched aboard had likely saved her life.
Excluding the two most recent attacks, there have been 33 recorded cases of shark bites in Australia so far in 2018, according to the Australian Shark Attack File of the Taronga Conservation Society Australia.
Less than 24 hours before the girl's attack, Tasmanian woman Justine Barwick had been attacked in the same harbour, causing her to lose a significant amount of blood.
The Whitsunday Islands, near the Great Barrier Reef, are a popular tourist destination.
"Fortunately he was able to assist in immediate treatment of the patient and to stabilise the serious haemorrhage that she had", Mackay local ambulance service network operations manager Tracey Eastwick, said.
She was airlifted to Mackay Base Hospital where she underwent emergency surgery.
It is understood she had been travelling on board vessel Miss Denero with her father and sister.
He called 000 as he headed to Cid Harbour from his position between Hamilton and Long Islands.
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A rescue helicopter scrambled to the region was just 15 minutes away from the scene due to an earlier operation they'd been undertaking.
Fisheries Queensland will send a patrol boat to Cid Harbour this afternoon to warn people not to swim.
Within hours of the second attack, Fisheries Minister Mark Furner announced he had activated special provisions to set up three drum lines in the area today.
She had been on a yacht before she was bitten and a doctor in a nearby vessel helped low the bleeding before a rescue helicopter arrived and took her to hospital.
The charter company on whose yachts the attack victims were staying is warning its customers to stay out of the water.
"In north Queensland, shark attacks are not that common".
'Fisheries is working with other agencies including the police and marine parks, ' the department said in a statement.
The child, believed to be a 12-year-old girl, is in a serious condition with injuries to their leg after being bitten at Sawmill Bay in Cid Harbour.
"Sharks can cover very large distances, so the chances of catching the same animal responsible for one of the attacks is very unlikely", she said.