Weather: Tens of thousands of Sydney residents flee homes as torrential rains pummel southern Australia

Flood warnings stretched across Australia's east coast on Tuesday and tens of thousands of Sydney residents fled their homes overnight as torrential rains again pummelled a large swath of the country.

Australia's eastern rivers were already near capacity following record downpours in several parts of Queensland and New South Wales states over recent weeks, cutting off towns, and sweeping away farms, livestock and roads.

Nineteen people have been killed, most either in flooded homes or in cars attempting to cross flooded roads, since the deluge began.

One northern NSW-based Kiwi woman Newshub spoke to lost her home and business in the floods.

"It's pretty... savage," Marie Barron said. 

"[I] thought we'd be okay when we fell asleep but the water was coming thicker and faster than expected so got out at 2:30am," said Barron as she took Newshub on a virtual tour of Lismore, NSW.

Barron's business was started in Auckland by her uncle. She's unsure when it can reopen.

"[There's] no point opening a business until I have a home," she said.

"[It's] just heartbreaking, I don't think I've ever cried so much."

A GoFundMe page to raise funds for Barron's clean up has so far attracted NZ$8036 in donations. 

Earlier, Australia Bureau of Meteorology forecaster Dean Narramore said minor to major flooding was occurring from the Queensland to Victoria border, a distance of more than 1555 kilometres.

"A tough 24 hours or even 48 hours ahead," Narramore said during a media briefing on Tuesday as he forecast up to 120mm of rains across Sydney over the next 24 hours, with the storm clearing by late Wednesday.

Heavy rains lashed Sydney overnight Tuesday with some suburbs receiving up to 200mm since Monday morning, exceeding March's mean rainfall of around 140 mm, triggering flash flooding and snap evacuation orders in the southwest of the city.

Emergency services estimated about 70,000-80,000 people in Greater Sydney were facing evacuation orders, although they do not expect everyone to follow them.

"People make decisions based on past history and I think this event has shown that there is no past history similar to this event," NSW Emergency Service Commissioner Carlene York told reporters.

Frustration was growing among many flood-hit residents in both states over slow relief and recovery efforts, with power and internet still down in several towns as emergency crews tried to clear roads to deliver essential supplies.

Prime Minister Scott Morrison, who is trailing in polls ahead of a federal election due by May, said on Monday more defence force personnel were being sent to flood-affected areas.

Reuters / Newshub.