Flooding is stranding residents of north Queensland communities already battered by Cyclone Debbie, as forecasters warn the state's southeast to also brace for a drenching.
Floodwaters have cut off the main roads in and out of the cyclone-ravaged towns of Airlie Beach, Bowen and Proserpine.
Motorists tried to leave the tourist town of Airlie Beach on Wednesday but came to an abrupt halt on Shute Harbour Rd, just a few kilometres from their destination.
The Proserpine River spilled over during Cyclone Debbie, all but swallowing road traffic signs and a railway crossing.
The ex-tropical cyclone will continue to generate very heavy rain over the Central Coast, Whitsundays, Central Highlands and Coalfields districts on Wednesday, the Bureau of Meteorology says.
Forecasters warn widespread daily rainfall totals of up to 250 mm are expected, with significantly higher totals possible locally.
A severe thunderstorm warning has also been issued, with fears of flash flooding in Mackay, Sarina and ranges west of Mackay in coming hours.
Earlier on Wednesday, the Pioneer River in the Mackay region was rising but authorities were confident no homes in the town were under immediate threat.
The Clark Range in the Pioneer River catchment area had recorded over 340mm of rainfall in the past 24 hours.
Mackay Regional Council Mayor Greg Williamson said some streets in the township of Mirani, on the upper reaches of the Pioneer River, had gone under.
The bad weather is expected to hit the southeast corner on Thursday and Friday before the rain depression that was Cyclone Debbie moves offshore.
Rainfall in the southeast is likely to be heaviest on Thursday evening into Friday morning, forecaster James Thompson told AAP.
But it's hard to say which particular spots will cop the most significant drenching, with totals of more than 200mm possible, he said.
"There's no real focus for this region," he said.
Authorities are releasing water from the Somerset Dam ahead of the predicted deluge.
Water Supply Minister Mark Bailey said on Wednesday the Somerset, which is northwest of Brisbane, was at 74 per cent, while the bigger, nearby Wivenhoe Dam was sitting at 67 per cent.
He said Seqwater was releasing water from Somerset into Wivenhoe to level up the dams but there was no concern about major flooding.
"Wivenhoe at 67 per cent has a large level of flood capacity available," he said.
It comes as Premier Annastacia Palaszczuk repeated her appeal for people to stay off roads, as emergency response teams try to get in.
"If you do not have to be on the roads until Friday, please stay off the roads. It will be some dangerous conditions and I do want all Queenslanders to be safe," the premier said.
Mr Bailey later said early warning community communications for a range of SunWater dams in the affected area had been issued.
"As expected, dams in the Bowen and Mackay areas are currently experiencing inflows and minor downstream flows are occurring," he said.
Significant increases in outflows were likely to occur in the next 72 hours, he said.
