The Bureau of Meteorology (BoM) has warned "significant flooding" is likely in parts of Queensland today, issuing a flood watch for the majority of the state amid intensifying rain.
Residents are being urged to take care in the wet weather after a man in his 20s was rescued from floodwaters in Mount Isa, in the state's north-west, last night.
The man was transported to Mount Isa Hospital in a stable condition with hypothermia.
9News understands the man became stranded and was forced to cling to reeds for 30 minutes.
READ MORE: Putin hails Victory Day
Heavy showers and storms are expected to lash much of the state today as the rain event deepens.
A severe weather warning has been issued for the Central and Northern interior.
An initial flood watch has also been issued for western and central Queensland and the central and north Queensland coast.
Longreach, in Queensland's outback, has already recorded 8.4mm of rain since 9am, Mount Isa 11.2mm, Townsville 12.4mm, while the Sunshine Coast airport has recorded 36.6mm.
Longreach local Jenny Gordon said the rain has not eased since midnight.
"It started around 12.15am and hasn't let up. Will measure (the gauge) at 9am," she said.
READ MORE: Scientists awed by 'penguin party' on Aussie beach
Today weather presenter Tim Davies said Longreach has a monthly average of 23mm of rain.
"Today alone, Longreach is forecast to get around 100mm, if not more," he said.
"The record-breaking rainfall really is set to intensify today."
READ MORE: The satellite images that cost these Aussie homebuyers $25k
Weatherzone said some parts of the state could be hit with "several month's worth of rain in a single day."
"This weather pattern is very unusual for May," the weather service said.
"A broad area of Queensland could pick up more than 100mm from this system and some areas could see more than 300mm."
Mayor of Townsville Jenny Hill said residents are on high alert, as "significant run-off" is expected tomorrow.
"The weather is already starting to roll in. We had about 50mm yesterday, which is pretty easy," she said.
"Tomorrow is the day that we expect to see anything up to well over 200mm.
"The big problem for us, the Bureau can only give us certain degree of accuracy. We can cope with 200mm if it falls throughout the day.
"It's very hard when you get 100mm, 150mm falling in an hour or two hours. That's the risk for everyone."
Residents in the coastal town are urged to "stay in place."
"We don't want people crossing getting out of their homes if roads are covered in water," Hill said.
More than two dozen catchments are "likely to be affected," BoM said. A full list can be found here.
Meteorologist Laura Boekel said "it doesn't take much rainfall for catchments to respond really quickly."
"That's when we can start seeing flash flooding and that's when we see the situations that become more life threatening," she said.
Ahead of the wild weather, Queensland Fire and Emergency (QFES) urged residents in affected areas to develop a "Plan B".
"So you know what to do if you're faced with flooded roads on your usual way to work, home, or school," it wrote last week.
"Remember, if it's flooded, forget it."
'Unusual' weather system behind big wet
The wet weather is being caused by an upper level trough over central Australia.
Rain will be heaviest over central parts of the state today, before the system sweeps across to the coast tomorrow.
Dangerous surf "up to three metres" is expected to develop in Queensland later this week.
Queensland's south-east is also on alert for heavy falls, however meteorologist Jackson Browne yesterday said the worst of the weather is expected across the central regions and north coast.
Areas in NSW are also expected to see heavy rain later in the week.
"The forecasting modelling really doesn't detail exactly how far south the heaviest of the rain will move," Davies said.
