Residents in western and southern Sydney are being warned to take care as storm cells bring damaging winds and large hailstones.
A severe thunderstorm warning was issued by the weather bureau just after 1.30pm on Friday.
Multiple fast-moving storms have hit the Penrith region, southwestern Sydney and near Wollongong, a spokeswoman told AAP.
The SES advises people to tie down any loose items in backyards or on balconies.
Motorists should avoid driving cars if possible.