Shoppers ran for cover as the ceiling collapsed inside the Westfield†shopping centre at†Mount Druitt†while a fast-moving and unpredictable†storm swept across Sydney's west.
A mobile phone video showed customers dashing†out of the shop as ceiling tiles caved in and water poured in from above.
The shopping centre was evacuated as NSW Fire and Rescue worked to assess the damage and stabilise the roof.
Awnings in the car park sagged under the weight of giant hailstones as the supporting poles buckled.
The collapse occurred after a severe thunderstorm pummelled Sydney and coastal NSW, bringing thunder, lightning, heavy rain and hail.
In half an hour, Penrith received 24 millimetres of rain.
A warning about a possible tornado was issued but cancelled late this afternoon.
The Bureau of Meteorology (BOM) said very dangerous thunderstorms were detected on the weather radar near Horsley Park, Penrith and Newcastle.†
The storms caused havoc on the roads and left some suburbs without power.
Jordan Notaro from the BOM said†while a tornado warning was†issued for†Western Sydney early on, the system appeared to have weakened.
?We haven?t had any observations of a tornado necessarily on the ground," he said.
?We have observed giant hail and as were going into the afternoon the prediction is we may see some more giant hail pushing across the Sydney basin as we head into the evening.?
AUSGRID said power has been cut to several hundred homes and businesses in Georges Hall, Yagoona, Bankstown, Bass Hill, Condell Park and St Ives.
Endeavour Energy spokesman Peter Payne said there are around 5,900†customers without power across Sydney suburbs, including †Mount Druitt, Minchinbury,†Oxley Park, Toongabbie, Seven Hills, Prospect, †Quakers Hill and Pendle Hills.
"Thankfully the storm (brought) lots of intense rain and golf ball sized hail in those regions but not a lot of wind," he said.
"So while we're estimating a restoration time of around 9.30 tonight for most people but hopefully the crews are out there patrolling now and hopefully the damage is not as significant as you may believe and we may be able to start restoring customers soon."
Mr Notaro from the BOM†warned that more severe†storm activity could be seen on Thursday tonight and Friday†around Sydney and further north to Newcastle.
"As†we head into the evening, however, we are continuing to be on heightened alert for potentially more severe storms particularly as we head into the evening into areas of Newcastle," he said.
"That particular thunderstorm is definitely moving out to sea but that definitely does not mean that we are out of the woods."
Other severe thunderstorms were detected on the weather radar near Wollongong, Bulli, Upper Mangrove, Engadine, Lake Macquarie, Brooklyn and Kurrajong.
The BOM reported 5-centimetre hail†near Wyangala Dam around 3:15pm and 3cm†to 4cm sized hail in the Blue Mountains, while†24mm of rain was recorded in 30 minutes at Goulburn.
The BOM warned that large, possibly giant hailstones, damaging winds and heavy rainfall†leading to flash flooding were likely.
© ABC 2021
04:58 AEDT The New South Wales government is being urged to issue a natural disaster declaration for parts of the Wollondilly Shire, south-west of Sydney, after a storm trashed the region over†the weekend.