A group of students on school camp at the Echo Creek adventure park near Tully remain trapped by flood waters and have received an emergency airdrop of food, clothing and medical supplies.
ICA CEO Rob Whelan said the "catastrophe" declaration means insurers would now prioritise claims from people affected by floods and storm-related damage.
Disaster recovery specialists will be deployed to the worst-affected areas once roads reopened, while policyholders needing help can contact the ICA's disaster hotline on 1800 734 621.
The state government has already declared a disaster situation in the region.
The declaration gives emergency services the powers they need to respond effectively to the flood.
Premier Annastacia Palaszcuk, who will travel to flood-affected regions on Sunday, said the full extent of the damage would not be known for weeks.
She said flooding would have a detrimental impact on banana and sugar cane crops, as well as the aquaculture industry.
"We will get the full assessments over the next few weeks about the impact on the economy and I think everyone should spare a thought for the farmers who are going to feel a huge impact," she said.
Ms Palaszczuk said one parent and one child had been evacuated from the school camp at Tully for pre-existing medical reasons, but that police had deemed it too risky to move anyone else.
She said the group was otherwise happy and healthy.
"No one else wanted to leave, they wanted to remain there," she said.
"They're in good spirits and we are in regular contact with them."
Flooding in Ingham, where more than 200 homes were inundated is easing, as the wet weather pushes further north to Cairns.
Major flood warnings remained in place for the Herbert, and Flinders rivers. Moderate and minor flood warnings were in place for many other rivers in the region.