Mini-tornadoes have ripped through communities in southeast Queensland, hitting one coastal town three times, leaving people injured, homes damaged and powerlines down.

And as ex-cyclone Oswald refused to budge from central Queensland, flooding around Gladstone led to the city being declared a disaster zone, with particular fears of a dangerously high tide on Sunday morning.

Meanwhile, residents in the small community of Winfield, north of Bundaberg, were issued an emergency notice and told to head to higher ground, with flooding imminent from the swollen Baffle Creek.

Authorities on Saturday evening were also concerned a dangerous storm tide could hit Moreton Bay coastal areas on Sunday morning, and issued an emergency alert for local residents.

The mini-tornadoes that hit on Saturday injured at least 17 people, damaged more than 150 homes, shops and other buildings in coastal towns around Bundaberg.

Burnett Heads and nearby Bargara were declared disaster areas after the twisters hit from 1pm (AEST), while one badly damaged a home at Coonarr.

Two people were critically injured when a giant pine fell on their parked car on the Esplanade at Bargara, while two homes were completely destroyed in the mini-cyclone that struck Burnett Heads.

At least 15 other people were treated for minor injuries after being hit by flying glass from broken windows and other debris.

Bargara resident Judith McNamara, who witnessed the tornado through her kitchen window, said it left a car in her yard with a tree through it.

"All of a sudden ... I looked up and a tree went flying through the air ... and the car went up," she told ABC radio.

A triage centre was set up outside a Bargara church to treat the injured, while an evacuation centre was opened at Bundaberg, about 15km away.

Burnett Heads was struck again twice at 6pm and 6.30pm, with two people believed injured in the second onslaught, with powerlines down and roofs torn from homes.

And the Bureau of Meteorology says the worst may be yet to come.

It has forecast the "strong possibility" of further tornado activity around Burnett Heads, Wide Bay and at Maryborough, south of Bundaberg, with emergency authorities warning people to batten down and stay indoors.

Power companies said it could take up to two days to restore electricity to the towns that were hit.

In the Gladstone area, torrential rain topped a metre in 48 hours and swelled the Boyne River to two metres higher than the previous record.

Tannum Sands and Boyne Island, at the mouth of the Boyne River, narrowly escaped inundation on Saturday but may not be so lucky when an extraordinarily high tide hits on Sunday.

"We're now getting ready for the next time when we think we'll have the biggest problem and that's at the high tide on Sunday morning," Gladstone Mayor Gail Sellers told AAP.

About 2000 people have been asked to evacuate.

Queensland Premier Campbell Newman told reporters a saddle dam off the Awoonga Dam was close to overflowing, which would put 500 homes in peril.

"That's my main concern," he said.

Mr Newman said dams west of Gladstone were experiencing unprecedented outflows and residents at Jambin and Goovigen had been ordered to take refuge on higher ground.

In the next few days about 300mm of rain is expected in Wivenhoe Dam catchment, upstream of Brisbane, and coastal areas could get as much as 500mm.

Mr Newman said controlled releases from the dam were continuing and there was no doubt it would be able to cope with the influx of rainwater in the coming days.

"We can absorb that flood," he said.

The biggest risk will come from suburban creeks on the Gold and Sunshine coasts and the greater Brisbane area.

"With all that heavy rain, flash flooding is definitely expected," Ken Kato from the Bureau of Meteorology told AAP.