Emergency crews have airlifted a man to hospital after he was attacked by a shark near Cid Harbour off the north Queensland coast — close to the area where two other people were mauled in September.

The Queensland Ambulance Service (QAS) said the man, believed to be in his 30s, suffered critical injuries to his leg and wrist.

The latest attack occurred while the man was swimming off a private boat near Cid Harbour around 5:30pm on Monday, the QAS said.

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It was dark by the time paramedics arrived by helicopter to treat the man, making their task more complicated.

It is believed crew on the boat were assisting the man when paramedics got to the scene.

Paramedics described the third attack in the area in less than two months as "the worst one yet".

CQ rescue crewman Ben McCauley described the scene and the man's injuries as "absolutely horrific".

The man was flown to Mackay Base Hospital for treatment, where he was rushed to surgery upon arrival.

"He'd suffered very serious bites, significant blood loss as well as cardiac arrest," Mr McCauley said.

"When we arrived he was already being treated by a paramedic from Hamilton Island, two off-duty doctors and an emergency department nurse from other nearby vessels."

Cid Harbour, on Queensland's Whitsunday Island, is a popular spot for charter boats and private yachts. ( Facebook: RACQ CQ Rescue )

On September 19, Tasmanian woman Justine Barwick was mauled on the leg by a shark while swimming in Cid Harbour on Whitsunday Island around 5:00pm.

She lost a lot of blood and authorities believed the presence of an emergency doctor on a nearby boat saved her life.

Less than a day later, a 12-year-old girl from Melbourne was bitten on the leg by a shark at Cid Harbour and rushed to Mackay Base Hospital in a critical condition.

In response to the attacks, Queensland Fisheries deployed drum line shark baits in Cid Harbour, and six potentially dangerous sharks were culled.

They included five tiger sharks, one of which was 3.7 metres long.

At that time, Fisheries was unable to say whether that shark had been responsible for either of the September attacks.

Fisheries Minister Mark Furner said Cid Harbour was not covered by the State Government's shark control program, which operates at 85 Queensland beaches.

Marine conservation groups attacked the Government over the capture and killing of the sharks.

A Humane Society International spokesperson said the response was futile.