The Insurance Council of Australia has declared the situation a 'catastrophe' and thousands of claims are expected.
Mr Turnbull called on the private sector to "pull together" to assist with the aftermath.
"Particularly the banks and insurance companies pull together, to provide support for the people of North Queensland who have had a very tough day and night in this," he said.
Mr Turnbull said Treasurer Scott Morrison and Assistant Treasurer Josh Frydenberg had reached out to the insurance and banking sectors.
"The treasurer and assistant treasurer have been in touch with the insurance and banking sectors to ensure they understand the how important it is to the government and indeed to all Australians that the banks and insurance companies are seen to be very supportive and responsive, compassionate, considerate and supportive in making sure that claims are met, that businesses are supported," he said.
Watch: Malcolm Turnbull pledges support for Queensland residents
Fears for the sugar industry
On Tuesday night Queensland Premier Annastacia Palaszczuk predicted "shock and awe" in the state when the full extent of the devastation wrought by the cyclone is revealed.
The premier said Debbie had caused vast losses, particularly in the farming and tourism sectors, with resorts on the Whitsunday Islands suffering severe damage.
There are serious concerns for the region's 2017 sugar cane crop which is estimated at $1.1 billion.
Queensland's tourism and farming sectors have taken a body blow and it will be some time before authorities can count the damage to homes and businesses from cyclone Debbie.
Heavy rain is continuing to hit flattened cane fields in north Queensland, in a region that supplies around half of Australia's $2 billion sugar industry.
A palm tree is fallen behind a motel at Airlie Beach, Tuesday, March 28, 2017. NO ARCHIVING Source: (AAP Image/Dan Peled)
Growers in the Mackay and Proserpine regions have been the worst-affected and there are fears the industry will take a severe financial hit from the storm.
Canegrowers CEO Dan Galligan says it's still been raining heavily today in some of the affected areas and flooding is occurring, and there are also serious concerns about the fate of the Wilmar-owned mill at Proserpine.
Watch: Cyclone Debbie leaving a trail of destruction
