Severe flooding in eastern Australia is believed to have left at least one person dead – a woman found in waters at a country homestead – and has prompted evacuations of tens of thousands of people.

Police said the body of a woman was found by a family member on a flood-affected property near Murwillumbah, a town in New South Wales.

"Inquiries are underway and a post mortem is expected to be conducted next week," a police spokesman said.

Torrential rains have left rivers overflowing across the states of New South Wales and Queensland and caused some of the worst flooding in more than 50 years. Authorities have warned to expect fatalities, telling residents to wave white sheets from their rooftops to alert rescuers.

Emergency services rushed to assist residents of homes engulfed by the rushing waters but said they had been unable to respond to all distress calls overnight.