Hunter Valley, Wollongong, and Sydney have suffered from golf ball-sized ice stones that started hammering the roundabouts at about 6 pm local time (7 am GMT) on 20 December.
Social media users have shared photos and videos of the natural disaster showing damaged cars and smashed roofs.
These hailstones at #Wamberal near #Gosford are bigger than golf balls #SydneyStorm. @2GB873 pic.twitter.com/M8FLJs1xtp
— Emily O'Brien (@EmilyC_OBrien) 20 декабря 2018 г.
@9NewsSyd look at this huge hail! pic.twitter.com/xqJKTu3bqI
— cassie (@cassieturnbull7) 20 декабря 2018 г.
Some of the hailstones looked like pumpkins or flowers, according to users.
Souvenirs from a very nervous trip to check the car #SydneyStorm pic.twitter.com/d7JLS7ht5b
— Michael Koziol (@michaelkoziol) 20 декабря 2018 г.
— Yulla_pyro (@PyroYulla) 20 декабря 2018 г.
— ZuZu (@ZuZPrincess) 20 декабря 2018 г.
READ MORE: WATCH Violent Storms Spawn Tennis-Ball-Size Hailstones in Rome
The Bureau of Meteorology has warned that the area remains dangerous, while the Insurance Council of Australia has declared the incident a "catastrophe".
Air Services Australia has reported that planes were not landing at Sydney Airport due to the storms.