Rescue teams delivered food and emergency supplies to Australians isolated by floodwaters Wednesday as authorities warned that swollen rivers posed an ongoing threat despite blue skies over the east coast following days of torrential rain.

Relentless downpours over the past week have caused "catastrophic" flooding in Australia's most populous state, New South Wales, with parts of suburban northwest Sydney still under water.

It was a 'miracle' no one had died in the worst flooding for some regions in a century, state Premier Gladys Berejiklian said, as sunshine brought welcome relief and some sodden residents began turning to clean-up efforts.

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