Parts of south-east Queensland have been hit with more than 400 millimetres of rain, stranding people in flash flooding and causing a second day of school closures on Friday.

Intense rainfall is predicted on Thursday afternoon, before the weather is expected to clear early on Friday.

The wild weather saw authorities:

Cancel classes and call for children to be picked up early from school

Urge shops and businesses to close by lunchtime

Announce free public transport so workers could get home

Warn the worst of the rain would hit tonight

Forecast clearer skies for Friday as the low pressure system moved offshore

There have been more than 3,600 calls for help to the State Emergency Service today, and more than 50 swiftwater rescues in south-east Queensland as ex-Cyclone Debbie dumped more than a month's worth of rain on the region in a single day.

A family of six were rescued as their home became inundated by rising floodwaters at Tanawha on the Sunshine Coast.

Firefighter Matt Foster said crews had to deal with dangerous conditions, but evacuated the family due to the ages of the children.

"They had a young baby, if the water was any stronger we would have left them there in situ," he said.

Schools were closed for the day, and Premier Annastacia Palaszczuk said they would remain shut on Friday.

Severe weather warnings are in place from Bundaberg to the south of Queensland.

Bureau of Meteorology forecaster Michael Knepp said 412mm had fallen in Upper Springbrook and Numinbah on the Southern Border Ranges in the 24 hours to noon on Thursday.

Over the same period in Brisbane, 221mm fell at Inala and Carroll Park, 212mm at Toowong, and 187mm at Mitchelton.

"Those numbers will increase over the next nine to 10 hours because it does look like the most intense rainfall we might experience will be just before this ends, which will be late afternoon and into the evening," he said.

He said it would start clearing around midnight and into Friday morning.

Another forecaster, Matt Bass, said winds of up to 125kph could occur.

'Stay off the roads'

Emergency services have urged people not to use the roads on Thursday evening, with authorities announcing free public transport to encourage workers to head home early.

Ms Palaszczuk urged parents to keep their children inside due to the risk of flash flooding.

"Please stay indoors. I need to have the road clear for our emergency services personnel if they do need to go to the assistance of people," she said.

"If there is rising waters on the roads, do not go through them."

4,000 sandbags filled an hour

Brisbane Lord Mayor Graham Quirk said the main concern was not river flooding — like in 2011 and 2013 — but overflowing creeks.

He said by 10:30am, about 40,000 sandbags had been distributed from the council's five depots, however an hour wait had been reported at Newmarket.

Mitchelton resident Chris was filling his four-wheel drive along with hundreds of other residents this morning.

He said the weather reminded him of Brisbane's devastating 2011 floods.

"I'm extremely concerned with what's going on. Of course, everyone is," he said.

No repeat of 2011 overflows

Dam capacities: Wivenhoe 69 per cent

Somerset 71.2 per cent

North Pine 52 per cent

Moogerah 97.4 per cent

Hinze Dam 107 per cent

Enoggera Dam 97 per cent

Massive rainfalls have already been recorded including in Numinbah in the Gold Coast hinterland, which received 186mm in three hours.

The band of rain spans almost half of the state.

Water Supply Minister Mark Bailey said dams in the south-east were operating normally, and the larger dams still had capacity.

"It will not be comparable to the 2011 situation — let's be really clear about that," he said.

"We believe it's absolutely manageable, and we are watching it closely.

"But of course predictions are one thing, actual rainfall is absolutely highly relevant and where it falls.

"If it falls one kilometre in a different place in an entirely different catchment, that affects everything."