As Central Queensland residents prepare for the biggest flood in 63 years, authorities are warning New South Wales locals starting their clean up that the danger is not over yet.

Forecasters are warning a major flood peak will hit Rockhampton overnight on Wednesday, reaching a level larger than the 2011 floods and potentially matching the February 1954 level of 9.4m.

"At that level, we would see around 5400 properties impacted including 3000 residential, 1500 commercial and potentially another 900 properties," Mayor Margaret Strelow said.

It's understood some local supermarket shelves have been left bare as residents scramble to collect supplies ahead of the floodwaters.


The Rockhampton Airport is also expected to close at midday on Monday.

The preparations come after the body of Eagleby man Nelson Raebel was found by emergency crews, becoming the Queensland's first victim following ex-tropical Cyclone Debbie.

Authorities were searching for three others: a man in his 60s who went bushwalking at Lamington National Park, 50-year-old Mondure man David Heidemann and 58-year-old John Frost from Mount Pleasant in Mackay.

Floodwaters are expected to start to recede in parts of Queensland's southeast, with about 30 homes in the Albert River catchment and 200 in the Logan River area likely to have been damaged.

Hundreds are also without power in the region - including suburbs such as Beenleigh, Eagleby and Loganlea - after Energex cut supply to stem the threat of electrocution.

In NSW, Lismore residents have been warned of hidden health risks in receding flood waters as they assess the damage after the worst flood in 43 years.

The northern NSW town was still contending with a moderate flood level of about 8m, as business owners in the CBD began to pile up damaged stock and ruined equipment outside.

"To be honest, it is like a war zone," Mayor Isaac Smith told AAP.

The State Emergency Service is yet to lift an evacuation order for the town, citing potential safety risks from contaminants and hidden hazards in the water.

"There are a lot of health concerns around what may or may not be in the water," Smith said.

Water levels in Lismore peaked within a metre of the 1974 record of 12.2m on Friday.

Two women, age 36 and 64, died after being caught up in fast moving waters, prompting Prime Minister Malcolm Turnbull to again warn communities to take care.