At about 7.30pm on Friday, police and emergency services were called to reports of a vehicle being swept away into floodwaters on Cherry Tree Road near the Bruce Highway at Kanigan.
On Saturday morning, following an extensive response, the body of the 22-year-old driver was found in the ute.
The driver has only been identified as a Sunshine Coast resident.
"We are tragically reporting that there has been one person that is now deceased, was trapped in floodwaters," Queensland Premier Annastacia Palaszczuk said on Saturday.
"We are praying that others are safe but we will be finding out further updates during the day."
Parts of the Bruce Highway were completely washed away due to the floodwaters, with several other roads closed across the state due to the damage and flooding.
Overnight, in the Wide Bay region, more than 650mm of rain fell, leaving some trapped in rising floodwaters.
"I can say that we do have a severe weather event at the moment," Ms Palaszczuk said.
The Bruce Highway north of #Gympie right now 🚨
Our crews are working hard to get the network open again after severe flash flooding across #WideBayBurnett as a result of ex #TCSeth overnight. pic.twitter.com/XjpjS7Xmr5
— Transport and Main Roads Queensland (@TMRQld) January 8, 2022
"I think everyone would know that we had ex-tropical cyclone Seth off our coast. It crossed over and has been sitting around this Wide Bay region and has not moved, is producing storms, and excessive rainfall."
Overnight, there were more than 700 calls for help, while 31 swift water rescues were launched.
Assistant Emergency Services Commissioner Stephen Smith said on Saturday incidents are "still being responded to".
"Out of those 31 Swift water incidents, 18 remain open," he said.
"We are having difficulty with access both on land and in air so we do urge community support in minimising to essential travel only."
Asked whether up to 15 people were unaccounted for, Mr Smith said efforts to access those whose whereabouts were uncertain were ongoing, with further updates expected during Saturday.
New cyclone brewing in wake of Seth
The Bureau of Meteorology is keeping an eye on a monsoon trough in the Coral Sea that is threatening to develop into a tropical cyclone by Monday.
"There is a moderate chance of a tropical cyclone forming in the northwest of the Coral Sea," BOM hazard response co-ordinator Brooke Pagel said.
The trough was set to develop into a tropical low and drift over the Cape York peninsula, intensifying when it enters the Gulf of Carpentaria.
"That's where we are expecting it to really ramp up and maybe form into a cyclone," Ms Pagel said.
It was thought Seth was petering out as it finally reached land after causing massive swells along the Queensland coast during the week.
Wild storms also lash Victoria
Down south in Victoria, hundreds of people called for help as wild storms brought about hail and flash floods.
In the 24 hours to Saturday, the State Emergency Service responded to more than 840 requests for assistance, mainly due to flooding or building damage.
"There were some events where rescues had to be enacted just with people that had been stuck in floodwater," SES duty officer Geb Abbott told ABC Radio.
On Friday, storms caused flash flooding in parts of Melbourne's western suburbs and the roof of a shopping centre in Point Cook caved in, collapsing under a heavy downpour.
In western Victoria, hundreds of properties have been left without power following the storms.
Meanwhile, the NSW Riverina is mopping up after a similar lashing.
Griffith was pelted with about 50mm of rain on Thursday, causing flooding on a number of roads and hail damage to roofs.
Residents were also forced to sandbag their homes, while the city's regional airport was shut down for 24 hours after the terminal was inundated.
Do you have a story tip? Email: firstname.lastname@example.org.