An emergency warning was in place for Sydney's northern beaches on Sunday morning, with residents at Narrabeen Lagoon and surrounds told to leave.
The evacuation was ordered the previous night as the dangers escalated quickly with rapidly rising floodwaters impacting properties, forcing locals and holiday makers to get to higher ground.
Floodwaters at Narrabeen are expected to take several days to recede.
The NSW State Emergency Service made 25 rescues of people trapped in floodwaters across the state, many in Sydney, as cars became submerged on inundated roadways.
At Great Mackerel Beach, an isolated outpost on the northern beaches accessible only by boat, a landslide damaged numerous homes and at least one person was injured.
The storm system claimed the life of a woman on Saturday after a tree branch fell on her car.
At least 1000 SES volunteers were on the ground on Sunday responding to weekend call-outs, with the busiest units in the south coast, Illawarra, Sydney and Hunter regions.
NSW SES spokeswoman Emily Barton told AAP rain had been experienced "far and wide" across the state.
As of 10am on Sunday, she said crews had responded to over 2100 incidents, mostly in Sydney and the surrounding area.
"We've got about 1000 SES volunteers that have been active during this operational response, and they remain ready to respond to any further calls for assistance," Ms Barton said.
"We've got high-clearance vehicles and flood rescue teams that are on standby, particularly through metropolitan Sydney and the Central Coast regions, where we're expecting to see the rainfall continue today.
"But storms are possible anywhere north of Wollongong and thunderstorms could bring those isolated, intense rainfalls that we saw late last night in the northern beaches and the Central Coast."
Ms Barton said clean-up efforts would continue over the next 24 to 48 hours, with further severe thunderstorms forecast for later in the week.
Warnings remain in place for hazardous surf on the east coast at beaches stretching from Newcastle to Batemans Bay, as well as the Eden coast.
Senior meteorologist Edward Townsend-Medlock said more heavy rain was expected from Sydney's northern suburbs through to the Hunter Coast on Sunday morning.
"Within that concentrated area is where you could get some of those more severe thunderstorm cells that we saw, for example, on the Central Coast," he said.
Queensland also copped wild weather as a band of thunderstorms rolled across the southeast, dumping up to 60mm and leaving about 11,000 properties without power.
More than 2000 properties were still without electricity at Laidley and Brightview in Queensland's Lockyer Valley region on Sunday as winds damaged homes and brought down trees.
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