Three people are confirmed dead after massive storms flooded rivers, uprooted trees and tore into beaches along Australia's east coast.

Rain and wind continue to batter southern New South Wales, Victoria and Tasmania.

Erosion at Sydney's Collaroy Beach has forced the evacuation of multi-million dollar homes, which are now in danger of collapsing.

The storms cut power to 86,000 homes in New South Wales at the weekend.

On Monday morning, a man's body was found in the Cotter River near Canberra. Police said the 37-year-old was caught in floodwaters at a river crossing.

Police divers have also retrieved the bodies of two men whose cars were washed off roads in separate incidents.

A 65-year-old man was caught inside his vehicle at Bowral, while another man was killed after his utility vehicle was washed off the road on Sydney's south-west fringe.

Flood warnings have been issued across several states, with northern Tasmania facing its worst flooding in decades on Monday.