Qld city flooded as new cyclone looms

The Queensland city of Maryborough has been inundated with water surging into the CBD through the stormwater drains amid a major flood.

Authorities had expected the river to peak in Maryborough above a major flood level of 10.5 metres, impacting about 80 homes on Sunday afternoon, after the remnants of tropical cyclone Seth dumped 600mm on the Wide Bay-Burnett region in two days.

A dozen pumps were deployed to drain the city centre, Fraser Coast Mayor George Seymour said in a Facebook post on Sunday night.

"We now have 12 pumps, each moving about 120 litres a second. We think the flood has reached the peak," he said in the post.

The levee was protecting the CBD until an underground stormwater valve failed just before 2pm, allowing floodwater to surge up through the drains and into the streets.

Police and Queensland Fire and Emergency Services issued an urgent emergency evacuation order for more than 30 inner-city blocks.

One person has already died in the floods, which came after intense rain pummelled the region on Friday and Saturday.

A 22-year-old's body was found in a submerged ute at Kanigan, north of Gympie, on Saturday.

A father and daughter were airlifted to hospital after surviving deep floodwaters for two nights by clinging to a tree in the Gympie region.

The pair had climbed on to the roof of their car after it began filling with water after becoming trapped between sections of floodwater on Friday night, RACQ LifeFlight Rescue said.

They were swept away by the rising floodwaters but managed to hang on to the tree until the waters subsided on Sunday, suffering exposure, dehydration and insect bites.

Police have received 177 calls for help, while QFES have responded to more than 50 water-related incidents and made at least nine rescues.

QFES Deputy Commissioner Mike Wassing urged people not to enter floodwaters or go sightseeing in Maryborough, where a local photographed a bull shark on Saturday.

"I do want to remind people about the dangers of floodwaters," he said.

"We've had the shark in the park, we've got contaminated water, you've seen what can occur with roads in the local areas and how dangerous that is," he said.

"Albeit the rain has stopped, the risk remains."

Meanwhile, a low pressure system in the Coral Sea has been confirmed as a category one tropical cyclone called Tiffany which is expected to cross the Queensland coast on Monday night.

Tiffany will continue to intensify as it approaches the far north Queensland coast, making landfall between Cooktown and Lockhart River.

The tropical cyclone is then expected to move into the Gulf of Carpentaria, potentially intensifying before impacting areas of the eastern Northern Territory from Wednesday.

Earlier on Sunday, Premier Annastacia Palaszczuk said emergency services were readying for the cyclone.