severe thunderstorm warnings were issued for blue mountains , the hawkesbury and sydney on saturday afternoon .
` large hailstones , heavy rainfall that may lead to flash flooding and damaging winds ' were forecast just after 3 pm .
hails stones up to 2 cm large were reported while social media users shared images of how the storm transformed various areas into snowfields .
seven buildings , including five 200m long factories , have collapsed under half a metre of hail in western sydney .
state emergency services attended over 800 calls for help , however the storm had cleared by 7 pm .