SYDNEY - Flights have been cancelled and residents were told to prepare for flooding as a dangerous storm approaches Australia's east coast.

The Bureau of Meteorology (BoM) on Tuesday morning issued a severe weather warning for almost the entire coast of the eastern state of New South Wales (NSW), including Sydney.

It said that a coastal low developing off the coast is expected to bring destructive winds and heavy rainfall across the state's southern, central and northern regions from Tuesday.

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Millions of residents of Sydney and the cities of Newcastle to the north and Wollongong to the south have been advised to expect winds exceeding 125 km per hour and six-hourly rainfall totals of up to 120 millimeters that could cause flash flooding.

"Winds could bring down trees or tree limbs, lead to dangerous driving conditions due to crosswinds or debris being thrown across the roads, and lead to power outages and possible damage to cars and property," BoM senior meteorologist Helen Reid said.

Qantas said it is anticipating disruption to services in and out of Sydney. Virgin Australia and Jetstar had cancelled 20 flights in and out of Sydney and Newcastle as of 8 am local time.

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The NSW State Emergency Service (SES) said that it has 1,000 volunteers on the ground to respond to any calls for help.

SES State Manager of Operations Dallas Burnes said that authorities were particularly concerned about flash flooding around workers' evening commute.

Motorists have been urged not to drive through floodwaters and boaters have been advised to avoid non-essential boating activity.