Queensland Police Commissioner Katarina Carroll blamed “extraordinarily difficult weather” for the tragedies.
“It has been a very tragic 24 hours due to the weather,” Carroll told reporters.
Severe weather has lashed parts of southeast Australia since Monday including Queensland and Victoria.
A woman, who is yet to be identified, was found dead late Tuesday after flash flooding receded at a camp ground at Buchan in regional Victoria.
Earlier on Tuesday, a 44-year-old man was killed by a falling branch at his rural property at Caringal in eastern Victoria.
Thunderstorms and strong winds have brought down more than 1000 power lines in parts of Queensland and left 85,000 people without electricity.