Two people are dead and five injured in Queensland as wild weather lashed Australia's east coast.
Most of southern Queensland and northern NSW was drenched, with a staggering 468mm of rain falling at Wooli River caravan park since Saturday 9am.
More than 500 residents have been evacuated from their homes due to flooding including residents in Coffs Harbour, which experienced its wettest June day on record, according to The Coffs Coast Advocate.
A flood watch has been issued for 23 NSW rivers and the State Emergency Service has responded to more than 3000 calls for help.
Severe weather conditions are expected to continue today with heavy rain and strong winds expected to make its way south along the NSW coast.
The extreme weather system is being blamed as a possible cause of a horror smash near Ipswich, west of Brisbane, that claimed the life of a man and woman on Saturday morning.
While the worst of the pouring rain and destructive winds is thought to have passed through Queensland, the conditions are expected to continue in NSW through today.
Bureau of Meteorology duty forecaster Kenneth Cheung said the heaviest falls in Queensland were experienced at Coolangatta, which has seen 280mm of rainfall since Saturday 9am.
Conditions in Sydney are expected to remain wet with a chance of thunderstorms in the morning and afternoon. Coastal winds are expected to get up to 70km/hour.
Rain should ease in the afternoon but will continue down most of the south coast for the remainder of today.
"Conditions are still quite severe and everyone needs to take care and stay up to date with the warnings for today," Mr Cheung said.
Severe weather warnings remain in Queensland, NSW and Victoria.
Five people were injured in a separate crash at Woodlands, south of Gatton, while there have been multiple reports of cars being swept away by floodwaters.
Beaches on the Sunshine and Gold Coasts were closed because of strong winds and high seas, while more than 220mm of rain was dumped on Upper Springbrook, in the Gold Coast hinterland, by Saturday morning.
The Bureau of Meteorology has also declared a severe weather warning along the entire NSW coast for what meteorologists believe is the first time in 30 years.
Authorities had warned that the storm would get more intense on last night, with king tides, winds of up to 125kmh and up to 200mm of rain expected to hit Newcastle and Sydney.
Threats to public safety prompted Vivid Sydney organisers to cancel a majority of lighting installations around Circular Quay and Martin Place, and urged those intending to visit to postpone.
The NSW State Emergency Service said it had received almost 300 calls for emergency assistance by early yesterday morning, mostly from homes in the state's north but also Port Macquarie, Coffs Harbour, Maitland and Gosford.
Queensland SES also received more than 200 calls for help, with 2500 properties on the Sunshine and Gold Coasts without power.
In NSW, an evacuation centre was set up near Fingal Head, south of Tweed Heads, amid fears the Tweed River could breach its banks.
NSW police have opened up the Public Information and Inquiry Centre to provide urgent updates on the weather and flooding across the state.
"We are going to experience over the next 48 hours increased rainfall and heavy winds - the public needs to take care in these conditions," Acting Assistant Commissioner Kyle Stewart said on Saturday night.
"Our message is clear - do not put your life and that of emergency services personnel in danger."
The Hawkesbury and Nepean Rivers and low-lying parts of western Sydney, including Richmond and Windsor, were a major focus for the SES, spokeswoman Stephanie Sullivan told AAP.
In southeast Queensland, where the wet weather has already contributed to two road fatalities, the Bureau of Meteorology has issued a severe thunderstorm warning for the Gold Coast.
The bureau said the severe storms were likely to produce even more heavy rainfall that could lead to flash flooding through Saturday night and into Sunday, especially in Coolangatta, Tallebudgera and waters off Tweed Heads.
- with AAP