A 12-year-old New Zealand girl holidaying with her father and sister received a life-threatening wound to her leg on Thursday afternoon at Cid Harbour.
The attack came less than 24 hours after Tasmanian woman Justine Barwick, 46, was also bitten on her left thigh while snorkelling in the same harbour.
Both remain in critical condition with Ms Barwick in Brisbane and the child at Mackay Base Hospital.
Fisheries Queensland will set three baited drum lines in the harbour on Friday in a bid to catch the shark or sharks responsible.
"It is possible that there's more than one shark involved in these unfortunate events," the department's shark control program manager Jeff Krause told the ABC.
"We don't normally go out and search for any sharks that may have been involved in a shark attack but due to the nature of these maultiple attacks, Fisheries Queensland is going to deploy three drum lines in a bid to try and catch some of the sharks in that area."
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Mr Krause said various types of whaler species as well as bull and tiger sharks can be found in waters around the harbour and he advised against swimming in or near Cid Harbour for the time being.
The last attack in the area was eight years ago.
Shark attack expert Daryl McPhee, from Bond University, said while the likelihood of being attacked by a shark is slim, the Great Barrier Reef has a higher population of sharks than other areas.
"That increases the chances of something happening," Associate Professor McPhee said.
"When sharks and people overlap in the water, that is when shark attacks occur.
"Sharks will bite things that they think are prey and sometimes they consider people prey."
