A 12-year-old girl suffered a "significant leg injury" near Cid Harbour, off Whitsunday Island, and was being airlifted in a critical but stable condition, according to the Queensland Ambulance Service.

The incident was reported just before 1.45pm and paramedics were on scene about 45 minutes later, thanks to a lift from the water police.

She was expected to arrive at Mackay Base Hospital about 3.40pm.

QAS Rockhampton operations centre manager Mindy Thomas said two paramedics and a doctor were at the scene with the RACQ CQ Rescue helicopter.

Ms Thomas said the helicopter was expected to collect the child from the boat once she had been stabilised and fly her to Mackay Base Hospital, where a trauma team was waiting.

The helicopter took off from Mackay about 2.10pm and had landed on the island by 2.50pm.

The initial shark attack, which left Tasmanian tourist and avid snorkeller Justine Barwick fighting for life in hospital, was reported just after 5pm on Wednesday.

Ms Barwick, 46, suffered severe leg and torso injuries when she was mauled by a shark in Cid Harbour as she swam with her husband and friends.

In that incident, one of the first paramedics at the scene credited the quick actions of a doctor, Mackay Base Hospital emergency department doctor John Hadok, who was on a nearby vessel, with saving her life.

RACQ CQ rescue crewman Ben McCauley said the shark had taken a "huge chunk" from the inside of Mrs Barwick's leg.

“She did suffer a lot of blood loss. There was quite a lot of blood around the boat,” he said.

“We were told there was arterial bleeding ... quite a big chunk of the leg taken, a few small puncture wounds on her calf muscle.”

Mrs Barwick was pulled from the water, transferred to a yacht and moved to a dinghy to be winched up by a rescue helicopter dispatched from the coastal town of Proserpine.

“The people on scene who got her aboard that yacht and quickly packed the gaping

wound to help stem the haemorrhaging undoubtedly saved her life," Mr McCauley said.

“She was very scared, cold and in shock - in and out of consciousness. She’s very lucky to be alive.”

The quick actions of emergency department doctor John Hadok have been credited with saving Ms Barwick's life.

She remained in a critical but stable condition in the Mackay hospital on Thursday.

Mrs Barwick is the operations manager with the Tasmanian community care organisation Family Based Care.

“She is an avid snorkeller and enjoys these times away with family and friends," Family Based Care chief executive Douglass Doherty said.

“Justine is a fighter: a fit, resilient woman who is an outstanding leader in the aged and disability care sectors."

She arrived at the Mackay hospital about 8pm on Wednesday after the helicopter stopped at Proserpine to pick up blood and to refuel.

- brisbanetimes.com.au with Luke Sayer