Authorities in Queensland said parts of the state received more than 600 millimetres (24 inches) in 24 hours.

With heavy rains continuing, residents in six flood-prone suburbs of Townsville, a city of around 200,000 people, were told to evacuate their homes Sunday.

The city's disaster management group coordinator Zac Dawes said 2,100 homes were under evacuation orders on Sunday evening.

But "about 10 percent" of the community did not heed the order, he said.

One of those was a woman in her 90s who has lived in Townsville all her life, according to her neighbour Shan Isis, who sought shelter at an evacuation centre.

"She's refusing to come to the evacuation centre because she believes the floods aren't going to be that bad, and she's seen heaps of floods before," Isis told the national broadcaster ABC.

Police said earlier that a woman died Sunday after the boat she was in capsized in the rural town of Ingham, around 230 kilometres (142 miles) from Cairns.

Queensland police superintendent Graeme Paine said the coming hours would be "really critical" for Townsville.

"Certainly for Townsville the indications are there will be an inundation that will impact people," he said.

Rising floodwaters forced the closure of the local airport and Townsville University Hospital to delay elective surgeries, as the state declared that around 100 schools were "unsafe for students to attend".

- 'Expect crocodiles' -

The state's premier David Crisafulli warned more rain was forecast in the coming days which could result in "record rainfalls".

The weather conditions were unlike anything the state had experienced "for a long time", Crisafulli said.

"It's not just the intensity, but it's also the longevity of it," he told the ABC national broadcaster earlier on Sunday.

"Take the precautions, prepare for the worst, listen to the advice -- please don't discount this," Crisafulli said.

The environment department has warned people to be on the watch for crocodiles that may move about in "search of calmer waters".

"Expect crocodiles in all north and far north Queensland waterways even if there is no warning sign," it said a statement cited by local media.

The heavy rain will continue in the coming 24 hours, with the Bureau of Meteorology warning some areas will receive 450 millimetres (18 inches) of rainfall.

Researchers have repeatedly warned that climate change amplifies the risk of natural disasters such as bushfires, floods and cyclones.