The size of the hail that just fell

The size of the hail that fell in Sydney
A series of extremely fast-moving storms have swept through Sydney, dumping hail and delaying flights at the airport.

UPDATE: The NSW SES has received more than 1400 calls for help since the storms began on Thursday afternoon.

Sydney metropolitan was the hardest hit area, Andrew Galvin from NSW SES told 10 Daily.

There have been about 350 requests for help in Hornsby in the city's Upper North Shore, while more than 270 calls have been received from Liverpool in the west.

"We have had huge demand on the telephones with a large number of calls," Galvin said.

Other areas severely affected were the Central Coast, Lithgow in the Blue Mountains and Narrabri in the north west of the state.

"We expect those numbers to continue to climb, and ask for patience. If you can't get through on the first go, call again," Galvin said.

The large number of calls mean the SES will prioritise urgent jobs overnight, and will call on help from its partners in the Rural Fire Service and Fire and Rescue.

Hail stones the size of coins fell across parts of Sydney, after a sweltering day across the city.

The storm came in from the south-west with the Bureau of Meteorology warning of "very dangerous thunderstorms"
detected near Camden and Picton.

Similar storms were forecast to hit Bankstown, Fairfield, Hurstville, Wollongong and Mona Vale during the afternoon peak on Thursday.

Hail stones of two centimetres were reported at Petersham, while Summer Hill reported three centimetres .

Berowra had reported stones of up to 5 centimetres just before 5pm.

The bureau issued a severe weather warning for heavy rainfall, damaging, locally destructive winds and large, possibly giant hailstones, for people in Sydney, Wollondilly and the Great Wollongong areas.

Other severe thunderstorms were detected on the weather radar near Hornsby, Parramatta, Sydney City, Sydney Airport, Sydney Olympic Park, the Sydney Harbour Bridge, and waters off Bondi Beach and Appin.

Sydney Airport said the weather was also causing some flight delays.

The storms swept through just after 4:30pm in most parts of the city, with the radar showing several areas of dark clouds, indicating hail storms.

Ausgrid said it was also working to restore power to around 2,000 homes in Epping and Carlingford, following the weather.

10 daily's own sports editor/weather nerd Ant Sharwood said the large hailstones have rings like onions because they have circulated in the atmosphere several times before they plummet to earth.

"They are carried by warm up drafts in thunderstorms because hot air rises, then plummeting, then ascending again and adding another layer of ice, before gravity finally wins."

Sydneysiders took to social media on Thursday afternoon, with one user saying it looked like snow in time for Christmas.