An urgent red alert warning was declared and thousands of people were urged to flee as a huge dam began over spilling amid intense flooding.
Tens of thousands of Sydney residents were told to evacuate as major flooding is causing chaos on the east coast of Australia.
Officials said the Manly Dam was starting to spill over and an evacuation was ordered - as New South Wales Premier admitted the State Government's response has not improved since Australia's devastating bushfires during 2019/2020.
"Residents in low-lying areas below Manly Dam need to evacuate immediately. LEAVE NOW," the State Emergency Service (SES) said.
New South Wales Premier Dominic Perrottet said an evacuation order affecting thousands of people was being given out due to the risk from the dam.
The dam is located in Manly Vale, on Sydney's northern beaches, and the order affect 800 homes and about 2,000 people.
“As a result of the Manly Dam beginning to spill, that will affect 800 homes and 2000 people," said Perrottet.
"As we have been saying during this period of time, and we will continue to repeat that message, if there is an evacuation warning in place, please get ready to leave."
Flood warnings stretched across the east coast on Tuesday and people have been forced to flee their homes overnight as torrential rains again pummelled the country's largest city, causing flash floods.
There are 59 evacuation orders in place in NSW which are affecting 40,000 people, while another 20,000 residents have received evacuation warnings.
SES Commissioner Carlene York said the dam is structurally secure.
She told a press conference: "The dam is currently spilling but I am informed by the engineers that the dam itself is safe.
"But the water will continue to come over and as these thunderstorms pass through, it may in fact increase."
The warning was later downgraded from red to amber in mid afternoon (local time) so people were told to be "watchful" and be ready to evacuate if necessary.
There is a severe thunderstorm warning in place for an area of north-east Sydney stretching from the northern beaches inland to Hornsby, where there is a risk of "life threatening" flooding and landslides.
NSW Premier Dominic Perrotte said there are major shortcomings from his Government as thousands of residents across NSW have been forced to evacuate after flooding continues to ravage the state.
Speaking to ABC Radio National, he said: "I take responsibility as the premier of the state...my role is to ensure people in these circumstances are kept safe."
He conceded there was not enough assistance provided by the Government to assist residents in fleeing their homes once waters began to submerge properties.
Mr Perrotte said: "From what I saw over the course of the week, had [local residents] not gotten into boats, then I believe the death toll would have been much higher."
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.
A man and a woman were found dead on Tuesday near an abandoned car in a stormwater canal in western Sydney, authorities said, while Queensland police confirmed the death of a man missing in floods since February 27, taking the death tally to 20 since the deluge began.
Most people were found dead either in flooded homes or in cars attempting to cross flooded roads.
Singapore's air force has deployed two helicopters to help flood recovery efforts, ABC reports. The city-state is also sending a relief package containing things like tents, blankets, ready-to-eat meals, water and medical supplies.
Bureau of Meteorology forecaster Dean Narramore said minor to major flooding was occurring from the Queensland to Victoria border, a distance of more than 966 miles.
"A tough 24 hours or even 48 hours ahead," Narramore said during a media briefing on Tuesday as he forecast up to 120 mm of rains across Sydney over the next 24 hours, with the storm expected to clear by late Wednesday.
