Communities south of Gladstone are seeing unprecedented flooding, with 900 homes evacuated.

Torrential rain from ex-cyclone Oswald has sparked a major flood crisis in the central Queensland city.

Gladstone Deputy Disaster Coordinator, Inspector Les Bulluss, says residents in the Boyne Island and Tannum Sands areas are seeing unprecedented flood levels.

He said a high tide of 4.25 metres, expected on Sunday morning, combined with 8.5 metres of water going over the Awoonga Dam wall was causing flooding in areas where that's never occurred before.

"At the minute we are seeing some quite significant, rapid rises down there into some yards," he told the ABC.

"One of our officers has had to perform a rescue of a person who in their state of intoxication thought it would be okay to walk across. That's the type of thing we're dealing with down there."

Boyne Caltex manager Trevor Falzon says his service station is up on a hill, but floodwaters have already cut roads nearby.

"I've never seen anything like this before," he told AAP.

Mr Falzon said his shop was a "madhouse" on Sunday morning as residents flocked to stock up on bread, milk and petrol.

"I had 100 bottles of milk yesterday and now they're all gone," he said.

"A lot of people are panicking and worried about their homes, but I think a lot of people do realise that they live in Queensland and these sorts of things are to be expected."

Gladstone Mayor Gail Sellers said floodwaters were starting to subside on Sunday morning, and Awoonga Dam was holding steady.

Earlier in the day, authorities said 8.5 metres of water was going over the dam wall.

Ms Sellers said she had not received any reports of homes being inundated in the Boyne-Tannum area so far.

"Things have turned out so much better than we were anticipating," she told AAP.

"I'm so relieved."

But Ms Sellers said the news was not as good for residents at nearby Baffle Creek, with supplies sent by helicopter into the area.

"They've got about 20 metres in Baffle Creek and it's up to the ceiling in some homes," she said.

"Baffle's an area that floods badly, floods often and floods for a long time."

Ms Sellers said there had been several rescue efforts at Baffle Creek and at Yarwun, north of Gladstone.

 

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