The clean-up after a night of wild storms has begun with power outages, flooding and transport delays triggered across Sydney.
Efforts to clear water, remove branches and debris and restore power to battered Sydney homes has begun after massive thunderstorms battered the city overnight.
Very dangerous thunderstorms were detected near Blacktown and Riverstone, the Bureau of Meteorology said on Thursday evening.
Emergency crews have had more than 600 calls for help after large parts of Sydney were battered by hail, heavy rain and ferocious winds.
And more bad weather is forecast on Friday, prompting warnings from authorities.
Images from the city's west showed golf ball-sized hailstones pummelling cars while almost 20,000 lightning strikes were recorded across the greater Sydney area.
Roads, trains and even flights were delayed and diverted away from Sydney's airports.
Mona Vale recorded 120mm of rain in just two hours from 10.45pm, and almost 20,000 lightning strikes were also recorded across the greater Sydney area.
"It was certainly a ferocious nigth for Sydney and its surrounds," the SES's Greg Murphy told Seven's Sunrise.
"What concerns us ... is there's potential for more storms today and into the weekend."
The wet weather isn't slowing down and could last until early or mid next week.
Friday is forecast to bring showers and thunderstorms to the state's east possibly extending to the northwestern slopes.
Showers are forecast on Saturday extending to northern inland areas while on Sunday showers will likely reach the far northern inland with a chance of thunderstorms in the north.
Sydneysiders are being urged to secure any loose items around their homes, and plan their travel around storm warnings.
The city has been battered by a number of major weather events in recent months.
In December, torrential rains and hail the size of tennis balls pelted Sydney, with the Insurance Council of NSW saying the damage bill was more than $600 million.