People across huge parts of NSW have been told to stay indoors as "very dangerous thunderstorms" stretch across hundreds of kilometres.
The warning came hours after the intense weather turned deadly when a woman was killed while driving on the Illawarra Highway at Macquarie Pass when the branch fell about 4pm today. A male passenger was also injured.
The NSW government's Hazard Watch put out an alert just before 9.30pm warning millions to stay indoors across Sydney, Gosford, Wollongong, Campbelltown, Morisset and Wyong.
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"Move or stay indoors clear of windows, bringing children and pets with you," the warning said.
"If you must travel, consider the consequences of road conditions and closures and make alternate arrangements for work, children, and travel.
"Use stairs instead of lifts in severe weather. You may become trapped if the power goes out."
The Bureau of Meteorology warned very dangerous thunderstorms were "likely to produce heavy, locally intense rainfall that may lead to dangerous and life-threatening flash flooding".
The storms were moving towards the north-west, Hazard Watch said.
At Pearl Beach, 133 millimetres of rain was recorded in the two hours to 3.43pm.
At Ettalong, 93.5 millimetres was recorded in just one hour to 2.22pm.
Another 67 millimetres was recorded at Cronulla South in the two hours to 5.35pm.
There have been hundreds of calls for help on a day of violent weather.
One of three rescued campers had hypothermia when police and the SES retrieved them from Geehi in Kosciuszko National Park in the Snowy Mountains on Friday night.
Across the state, SES volunteers have responded to hundreds of weather-related jobs, particularly in the South Coast, Illawarra, Sydney and Hunter regions.
Volunteers helped several people trapped in their cars as flash flooding hit Albion Park, Picton and Marulan in the Southern Highlands.
NSW SES Superintendent Matt Kirby reminded people to put safety first.
"This weather can produce heavy rainfall and strong winds, so we remind people not to drive through floodwaters and be wary of where you park your vehicles as tree branches can fall at any time," Kirby said.
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"Download the Hazards Near Me app to stay up to date with any warnings that have been issued."
Heavy rain has already drenched parts of the state in the worst storm of the summer.
In Moruya, almost 200 millimetres of rain fell in the 48 hours to 9am on Saturday.
It was warned that the slow-moving pressure system could bring up to 120 millimetres of rain in some parts of the NSW coast over 24 hours.
Heavy rain and damaging winds were likely to continue in Sydney, the Blue Mountains, the Illawarra and Shoalhaven.
Severe thunderstorms were also likely across the Central Coast and Mid North Coast regions.
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