A 12-year-old girl has been attacked by a shark at the same Queensland island where a Tasmanian mother was mauled less than 24 hours earlier.

A rescue helicopter flew to Cid Harbour in the Whitsunday Islands region around lunchtime on Thursday to retrieve a "another shark bite patient", the RACQ CQ Rescue service tweeted, after a girl was bitten on the leg.

#RACQ #CQRescue now headed to Cid Harbour to retrieve another shark bite patient, 2nd in 24 hours. pic.twitter.com/S1iARjpswJ — RACQ CQ Rescue (@cq_rescue) September 20, 2018

The Queensland Ambulance Service said the girl was in a serious condition with a "significant leg injury".

#Update - Paramedics are treating a female child in a serious condition with a significant leg injury after being bitten by a shark in waters near Cid Harbour. A critical care paramedic is at the scene with the @cq_rescue helicopter. — Queensland Ambulance (@QldAmbulance) September 20, 2018

She was taken to Mackay Base Hospital.

On Wednesday evening, Justine Barwick, 46, was mauled while snorkelling nearby, and is lucky to be alive.

Ms Barwick, a mother of two, would likely have bled to death from a severe wound to her left thigh without the quick-thinking actions of people in nearby boats.

A rescue helicopter scrambled to the region was just 15 minutes away from the scene due to an earlier operation they'd been undertaking.

The hovering chopper drew the attention of John Hadok, an emergency department doctor from Mackay Base Hospital, who was sailing nearby and soon joined the effort to save Ms Barwick's life.

Dr Hadok's direction ensured correct first aid was given to Ms Barwick, allowing her to be safely winched into the helicopter.

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.

"The original first aid was actually really well done," Mr McCauley told reporters on Thursday.

"We actually didn't have to do anything with the leg, it was pretty much tourniqueted up, bandaged up and bleeding had stopped. They'd done a really good job."

Although he didn't see the wound, Mr McCauley was told Ms Bariwck had "quite a big chunk of leg taken" and had suffered arterial bleeding.

She also suffered puncture wounds to her calf muscle.

The helicopter then stopped at Proserpine to refuel, allowing blood from a local hospital to be transfused and other medical treatment given.

Just after 8pm Ms Barwick arrived at Mackay Base Hospital where she remains in a critical condition on Thursday morning after overnight surgery.

Her husband Craig is at her bedside.

Ms Barwick works for non-profit Family Based Care in Burnie and had travelled to the Whitsundays on a holiday with her husband and friends.

Family Based Care chief executive Doug Doherty said Ms Barwick and Craig were regular visitors to the popular tourist destination in the heart of the Great Barrier Reef.

"It didn't surprise me, because she is such a fighter, when she was being taken off the rescue helicopter and taken into hospital she was telling them what she was allergic too and still able to give directions," Mr Doherty told AAP.

"That sounds like Justine to me."