Premier Annastacia Palaszczuk has urged parents to collect their children from schools from north of Brisbane to Bundaberg, as soon as it is safe to do so, on Thursday.

"These are unprecedented times," the premier told reporters.

"It is extremely unstable weather conditions and, as a precaution, we would like our people to collect the children when they think it is safe to go out on the road and do so."

The Bureau of Meteorology warns the line of storms will be "dangerous and potentially life-threatening" with catchments already saturated.

The town of Grantham is being evacuated as a precaution ahead of possible flash floods after the nearby Lockyer Valley recorded 80mm of rain in 24 hours.

Deputy Police Commissioner Shane Chelepy said emergency services and Australian Defence Force troops were door-knocking in Grantham to ensure residents were ready to flee.

"We've already had 80mm there, so we would only need one more severe storm system over that which would cause issues there, and that's the same right across the areas that have been mentioned today," he said.

The first storm cells struck overnight after the worst floods in the decade, which have killed nine people and damaged more than 17,000 homes and businesses.

Cyclonic wind gusts of up to 93kmh brought down trees and power lines and sparked another wave of 360 calls to the SES for help.

The premier warned conditions would be continue to be unstable for the next 24 to 48 hours across the entire southeast.

"I'm asking people tomorrow to think about not being on the roads and staying at home, the schools will open for children of essential workers," Ms Palaszczuk said.

"I've lived in Brisbane essentially all my life and I haven't seen storms and floods like this all being thrown at us at once.

"We'll get through it together. "

Bureau of Meteorology forecaster Laura Boekel said the thunderstorms bring a chance of more flooding and flash-flooding across the southeast in the next 24-48 hours.

"This is a very dangerous and potentially life-threatening situation for southeast Queensland," she told reporters.

She said the Lockyer and Bremer rivers and Laidley and Warrill creeks are likely to flood and there will be moderate flooding at Ispwich during the day and major flooding by Thursday night.

Six-centimetre hail pummelled Windera, north of Brisbane, while stones 5-6cm smashed into the southern town of Inglewood.

Brisbane city recorded an intense 48mm of rain in just 30 minutes.

"So that's a severe storm with some very intense rainfall. And what we have seen can indicate what we can expect for the rest of the day," she said.

"We also saw giant hail - unlike the event we have seen over the past week, this isn't a widespread area rain, it's severe thunderstorms, and with severe thunderstorms come severe hazards and phenomenon."

Ms Boekel said the main concern for Brisbane was not the river, but the creeks where there is potential for flash flooding.

"They cannot take any more rainfall. They are what we call saturated."

Police are still searching for an elderly man who fell from a boat into the swollen Brisbane River near Breakfast Creek on Saturday afternoon.

Brisbane Council had been gearing up to mobilise more than 10,000 in the Mud Army 2.0 to clean up the city after it was swamped with floodwaters this week.

Australian Associated Press