A young girl has died and three hikers have been pulled from floodwaters after wild weather triggered hundreds of calls to emergency services in New South Wales.
The centre of a powerful low-pressure system began crossing the coastline between Nowra and Batemans Bay about 5am on Thursday.
The system has triggered several severe weather warnings for flash-flooding, damaging winds and hazardous surf. It also whipped up at least two tornadoes, including one near Young in NSW's South Western Slopes.
The State Emergency Service (SES) released footage of the dramatic rescue of three hikers from rising floodwaters at Wattamolla, in Sydney's Royal National Park.
Meanwhile in Tenterfield, an SUV carrying a 50-year-old woman and an 11-year-old girl crashed into a tree before plunging into a dam about 3pm on Wednesday.
The girl was pulled unresponsive from the water and pronounced dead at the scene while the driver, a 50-year-old woman, was taken to hospital in a stable condition.
In the 24 hours to Thursday morning, the NSW SES received 854 calls and 34 rescue calls from the metropolitan and southeastern regions of the state.
The Bureau of Meteorology's Angus Hines told Daily Mail the system would gather strength as it approached the coastline.
Overnight, the largest amount of rain fell along the Illawarra Coast, with totals between 120mm and 150mm recorded in the region.
Sydney recorded almost 100mm of rain in the CBD since 9am on Wednesday, 30mm more than the city's rainfall average of 60 to 70mm for the entire month of September.
The city experienced numerous minor flooding incidents on Wednesday night, with some main roads inundated in Sydney's east.
Images showed the water level reaching car boots on Anzac Parade in Randwick.
One video captured the moment commuters on the 333 bus headed to Bondi Beach were forced to sit cross-legged on their seats as water sloshed around on the floor.
One of the entrances to the SCG and Entertainment Quarter had to be closed as drivers struggled to keep traction in deep waters at Moore Park.
The rain is expected to finally ease in Sydney by Thursday evening.
An expert meteorologist warned the complex low could intensify as it neared the coast, having crossed inland NSW.
In the city's south, the rain is expected to ease by the afternoon, with strong winds beginning to move east in the evening.
NSW SES State Duty Commander, Assistant Commissioner Dean Storey issued a warning amid the floods.
'Flash flooding can occur quickly and without warning. We implore motorists to never drive, walk or ride through floodwaters - if you come across a flooded road, turn around and find an alternative route,' he said.
Several weather warnings remain current around the state, including minor flood warnings for the Nepean River, the Georges River, the Namoi River, the Cooks River, the Macquarie River to Bathurst, and the St Georges Basin.
Hazardous surf warnings were issued for the Macquarie Coast, Hunter Coast, Sydney Coast, Illawarra Coast and Batemans Coast - with many to remain in place on Friday.
Strong marine wind warnings are in place for the state's entire coastline, with gale warnings issued for the Coffs, Macquarie, Hunter, Sydney, and Illawarra coasts.
The weather bureau is expecting the system will begin tracking to the northeast over the Tasman Sea throughout Thursday.