No deaths were reported, but thousands of people have been rescued by emergency services in recent days. About 18,000 people have been evacuated with authorities expecting about 15,000 others to join them.
Houses in Sackville North, a suburb 80 km (50 miles) northwest of Sydney, were left partially submerged by the swollen Hawkesbury River.
"There was a flooding last year but not this bad. So we've got a place on the other side of the river and we just came over to move our van onto high ground and we're trapped on the other side of the river, with the landslides, so we've been there for a couple of days," said Alicia Pitt, a resident who was rescued early with her family from their holiday cabin on the river.
The national weather agency has posted severe weather warnings in every mainland state or territory but one, affecting around 10 million people in the country of 25 million, across an area the size of Alaska.