Intense rain and damaging winds are expected to sweep across parts of the ACT and NSW on Friday, the Bureau of Meteorology has warned.
Flights into and out of Sydney Airport were cancelled or delayed because of fierce winds and heavy rain. Runways remained open there through the morning but the authorities were monitoring the situation, with the expectation that winds would pick up in the afternoon.
Canberra Airport was geared up to take diversions if the weather worsened.
"When the weather turns bad in Sydney, we quite often have diversions," Canberra's director of aviation Michael Thomson said.
"We are prepared for them. If they are required to come to Canberra, we are all set to accommodate them."
Sports people were also watching the weather. The fear of turning Canberra's sportsgrounds into mud pits in the opening round of the season could force the ACT government to close venues across the city. At 2pm, the government decided not to close them allowing season-opening games to go ahead.
NSW residents are being urged to avoid taking unnecessary risks as the state braces for "a significant weather event".
As of 3.45pm, Canberra had received only 5mm since the night, even though up to 40mm was forecast for Friday.
More than 100mm of rain had already fallen in 24 hours over Sydney by 10am, with warnings for possible life-threatening flooding and damaging winds stretching from the Hunter to the South Coast.
The bureau updated its severe weather warning on Friday, forecasting the trough over eastern New South Wales to deepen "under the influence of a slow-moving upper-level low over central New South Wales".
"Areas of heavy rain and gusty showers are forecast to develop south of about Newcastle today, including over the ranges and tablelands," the bureau said.
"Severe weather is expected to gradually shift south overnight, easing later on Saturday as the trough moves east to the Tasman Sea.
"Heavy rainfall which may lead to flash flooding is forecast for the southern parts of the Hunter to the Sydney Metropolitan, Illawarra, and Central Tablelands districts developing from the late morning, then shifting south to the remaining districts overnight into Saturday morning while easing from the north."
The warning is primarily for NSW, but includes a small part of the north and southeastern tips of the ACT border.
Canberra is expected to receive up to 40mm of rain on Friday and up to 45mm on Saturday before easing.
"Severe weather is forecast to ease below warning thresholds by Saturday afternoon," the bureau said.
Sheep graziers near the edges of the ACT have also been warned about the risk of losing livestock in a severe weather warning issued by the Bureau of Meteorology.
"There is a risk of losses of lambs and sheep exposed to these conditions," the bureau said.
The rain is expected to ease in Canberra from Sunday, when there's a 60 per cent chance of rain and a forecast of up to 3mm.
NSW Flood Watch has also issued an alert for a risk of minor flooding of the Queanbeyan and Molonglo rivers.
In NSW, the SES has carried out seven flood rescues among 550 calls for help across the state in the past 24 hours and NSW Premier Chris Minns said that number was expected to rise in the coming days.
"This is a significant weather event," he said on April 5.
"It's very important that everyone in NSW listens to the latest broadcasts for updated warnings particularly in your local region.
"It's most important that you don't take unnecessary risks at the moment, particularly travelling through floodwaters."
NSW SES commissioner Carlene York said emergency resources were in place to help affected communities.
She also asked residents to heed the warnings and to put off unnecessary trips with dangerous conditions on the roads.
