Sydney's extremely heavy rains forced thousands to flee "dangerous" floods Monday as the city's largest dam spilled torrents of water.

On the third day of torrential east coast rains, emergency workers said they had rescued more than 80 people since the previous evening.

Many people had been trapped in their cars trying to cross flood-swept roads or were unable to leave homes surrounded by rising waters.

About 32,000 people ordered to evacuate

About 32,000 people were ordered to evacuate or be ready to flee across New South Wales, the emergency services department said, with the army sending 100 troops to help operations in the storm-battered state.

"The ground is saturated, the rivers are fast flowing, the dams are overflowing," said State Emergency Services commissioner Carlene York.

"It is particularly dangerous out there," she said at a news conference.

Large volumes of water burst from Warragamba Dam

Mud-brown river waters transformed a large stretch of land into a lake in the southwestern Sydney suburb of Camden.

Large volumes of water burst from the Warragamba Dam, which has been spilling excess water since Sunday. The huge concrete dam lies on the western outskirts of Sydney and provides most of the city's drinking water.

Heavy rains in New South Wales may persist for at least another 24 hours, forecasters said.

Similar events likely to occur 80% more often by end of 21st century

Australia's east coast has suffered repeated flooding in the past 18 months.

More than 20 people died only in March this year as floodwaters reached rooftops and swept cars off roads.

The current weather system over Sydney is being fed by warm, wet air from near the equator, explained Kimberley Reid, an atmospheric scientist at Monash University. 

Rainfall in eastern Australia is highly variable, making it hard to pin this event to climate change, she said.

"However, our research of the March 2021 Sydney floods found that similar events over Sydney were likely to occur 80 percent more often by the end of the 21st century," the scientist pointed out.

Australia must prepare for more floods

In the same context, New South Wales Premier, Dominic Perrottet, told a news conference that Australia must prepare for more regular flooding events.

"There is no doubt these events are becoming more common," he said.

The Premier stressed that "Governments need to adjust and make sure that we respond to the changing environment we find ourselves in."