Flooded rivers continue to rise across New South Wales and Queensland after three people were confirmed dead and three others missing following torrential rains caused by Cyclone Debbie.

Queensland police have warned that the Logan River, which runs through Beenleigh south of Brisbane, is yet to hit peak flood levels.

There is also a serious threat of further flooding in the city of Rockhampton until Wednesday.

Police have confirmed that the body of a 77-year-old man who went missing from Eagleby has been found, taking the death toll from the floods to three people.

On Friday, police discovered the body of a woman who disappeared in floodwaters near Murwillumbah just south of the Queensland border.

And a 64-year-old woman, whose vehicle was swept off a causeway on a property in Gungal, in the Hunter Valley south of Sydney was also found dead on Friday.

Watch: Flood effected NSW residents evacuate

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NSW Police also said the body of a 45-year-old man was located at a caravan park in south Murwillumbah on Saturday, although it is yet to be confirmed that the death is related to the flooding.

Police Commissioner Ian Stewart warned there was "still a major risk to the community around Logan and further south caused by that flooding situation".

Rockhampton, with a population of over 80,000 on the Fitzroy River, was expected to suffer flood levels not seen for a century and Stewart urged residents in low-lying areas to leave.

"By Wednesday, we will be at peak flooding in Rockhampton," he said.

"It will be a gradual rise, so I encourage people to move now."

Tens of thousands of people have been evacuated from a string of towns in Queensland and New South Wales as the floods move south towards Ballina, cutting roads.

Grim scene

Others have tried to stick it out to save their properties.

Casey Bently, a 47-year-old mechanic from North Maclean appeared visibly upset as she looked at her house, submerged to the roof.

"We got as much out as we could in the short time that we had," she told AFP.

"People have lost everything. I'd only just finished renovating the house, and it is all gone again now."

Some residents on Cabbage Tree Island in northern NSW have planned to stay in their homes as flooding approaches, despite orders to evacuate.

Watch: Flood waters increasing in Chinderah

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Kathleen Cameron has 19 pets and says she's not going to adhere to flood evacuation orders until they are all high and dry.

The woman was among the residents told to leave the small Cabbage Tree Island in northern NSW on Saturday.

But when the SES co-ordinated bus pulled up, Ms Cameron was standing on her verandah with some of her eight dogs and eight cats.

Her turtle, Winston, and two birds were inside.

"It'd kill me (if they were harmed)," she told AAP in the small the Aboriginal community on Saturday.

"I'm not just going to leave them by themselves."

'Very dangerous time'

Prime Minister Malcolm Turnbull called on residents in affected areas to exercise caution.

"In many parts of the country you will see floodwaters continuing to rise over the next days," he told reporters.

"This is a very dangerous time in these flooded areas.

"I want to say to everybody who is affected by these floods – do not go into flooded waters. Do not cross flooded roads."

Trapped on a roof

A Lismore resident described how he, about 10 neighbours and three dogs spent hours on a roof when near-record flooding hit the northern NSW town.

James Lewry, 27, said the group spent six hours on a roof in the CBD, before friends came to the rescue on Friday afternoon.

He said he was forced to flee to the top of the factory after water rose to the ceiling of his two-storey house.

"They (waters) rose so quickly we couldn't really develop a steady plan as to what to do," he told AAP on Saturday.

"When that stuff sort of happened it was incredibly stressful and quite incredibly scary at points."

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Category four Cyclone Debbie hit northeastern Australia on Tuesday between Bowen and Airlie Beach ripping up trees and causing widespread damage that is still being assessed.

It was downgraded to a tropical low as it tracked southeast still packing high winds and dumping huge amounts of rain all down the east coast to Sydney and beyond before blowing out over the Tasman Sea.

Lismore, south of Murwillumbah was among the worst flooded towns on Friday with Tweed Heads, Kingscliff and Murwillumbah also subject to evacuation orders.

In areas further north where the cyclone made landfall, water and power were still being restored.

Bowen, Mackay and the Whitsunday islands bore the brunt of the cyclone and nearly 40,000 homes were waiting to be re-connected on Saturday.

The military has mobilised 1,300 soldiers for the clean-up with helicopters and planes deploying to restore infrastructure and supply emergency food, water and fuel.

The Insurance Council of Australia declared the Queensland and northern NSW regions disaster zones, adding that the damage bill could top $1 billion.