The body of a man was found in a car trapped in floodwaters in Australia's southeast on Friday, raising the death toll to four, after three days of incessant rain cut off entire towns, swept away livestock and destroyed homes.

Officials in Australia's most populous state made a natural disaster declaration in response to record rainfall.

Four people have died and several were missing as major flooding in New South Wales (NSW) left about 50,000 people isolated by floodwaters. The record rainfall, now declared a natural disaster, has been caused by a slow-moving area of low pressure and is greater than any in living memory for some residents, according to local authorities.