A man's body was found in Canberra's Cotter River after the four-wheel drive he was in was swept away. Police also confirmed divers retrieved a 65-year-old man's body in Bowral on the Southern Highlands as well as another man's body in the Sydney suburb of Leppington. Both had been swept away while driving through flood waters on Sunday.
Police in Tasmania also said they had grave concerns for two people missing in Ouse and Latrobe.
In Canberra, Police were called to rescue two men stuck in flood waters on Sunday about 4.30pm and found another vehicle in trouble, which Station Sergeant Harry Hains said was washed away before they had a chance to rescue him.
"During the course of trying to ascertain a safe method to extract that male, the vehicle has shifted and the male has disappeared from view along with the vehicle," Hains said at a press conference on Monday.
"A short time later, police, along with State Emergency Services and ACT Fire and Rescue located what we believed to be a a body stuck in raging floodwaters on an island in the middle of the river."
It wasn't safe to retrieve the body of the man, 37, until Monday morning, with Hains describing the water as "extremely strong, savage, with a lot of debris and large logs".
Hains said that while police did not know the reason he was attempting to cross a flooded river, the region was a four-wheel driving spot.
"Extreme weather conditions, we've experienced, do lead adventure-seeking type people to seek mud with their four-wheel drives," Hains said.
"There is no risk worth taking to cross a flooded river to go and seek some piece of dirt to drive your four-wheel drive on."
State Emergency Services ACT chief Conrad Barr said "this is the most serious and regrettable incident we've had to attend" in a weekend of extreme weather.
In NSW, of the 9200 calls for help since Friday night, SES spokesperson Stephanie Sullivan told The Huffington Post Australia more than 280 were flood rescues.
"Across the state, there were vehicles caught in flood water," Sullivan told HuffPost Australia.
"A really common feature of east coast lows is there will be really heavy rainfall in a very quick period of time and people take chances to drive through flood waters."
Sullivan also said Sydney's Northern Beaches were slammed with coastal erosion and flooding, causing the evacuation of more than 100 people in Collaroy and Narrabeen.
State Emergency Service Queensland said there were more than 1120 storm call-outs across the state with 170 from the Brisbane City Council area while in Victoria, spokesman Stefan Delatovic said Victoria SES staff were prepared for flooding.
"It does seem that Victoria has avoided the worst of the storm but there's a lot of rain in the far east so we're watching places like Gippsland for flooding," Delatovic said.
"There's a chance for short, sharp flash flooding and gradual flooding as the rain continues to fall."
Prime Minister Malcolm Turnbull thanked emergency services for their contribution.
"They are out there today and they were out all last night putting their lives on the line, risking their lives to keep Australians safe and we thank them and we honour them," Turnbull said.
Tasmania meanwhile is bracing for the worst as the storm moves south, with a flood warning in place for all rivers, and evacuation centres are receiving people.