Days of intense rain have caused flash flooding in Australia's eastern states of Queensland and New South Wales, claiming at least eight lives with some people still missing, while evacuations, power outages and school closures have added to concerns.

Queensland State Premier Annastacia Palaszczuk on Monday compared the severe weather to cyclones the state has faced in the past, calling it an "unpredictable rain bomb."

"No one has seen this amount of rain in such a short period of time over our entire southeast catchment zone," Palaszczuk told reporters in the state capital Brisbane on Monday, where at least 15,000 homes are expected to have been affected by the floods.

The death toll rose to eight on Monday, after a man believed to be in his 50s died when his car was washed away in floodwaters, Queensland Police said. A number of people are still missing, authorities added.

The Queensland town of Gympie about 170 kilometers north of Brisbane has been one of the worst-hit by the floods, after the Mary River peaked at 22.9 meters on Sunday morning, the highest level since 1893, according to local media.

While intense rain began to ease in southeast Queensland on Monday, meteorologists warned the risk for significant flooding is "still very real," with water levels expected to remain high for several days.

Attention is now turning to Australia's most populous state of New South Wales, as the weather system moves south across the state border. Communities in the state's north have been ordered to evacuate, with some areas already hit hard by flash flooding.

In the town of Lismore, just south of the Queensland border, residents resorted to climbing onto building roofs as floodwaters rose rapidly to the highest level ever recorded, and continue to rise.

The Australian Defense Force has been deployed across flood-affected areas to assist with rescue efforts, and disaster payments are being made available for impacted communities, Australia's Prime Minister Scott Morrison said Monday.