The warning was broadcast at about 12.30pm, and covers the next several hours which, according to the BoM, may produce "damaging winds, large hailstones and heavy rainfall that may lead to flash flooding".

VIDEO: The storm rolling towards Forest Reefs ...

The State Emergency Service advised people should move vehicles under cover or away from trees, and secure or put away loose items around homes, yards and balconies.

It's also recommended residents keep at least eight metres away from fallen power lines or objects that may be energised, such as fences.

Residents are asked to report fallen power lines to either Ausgrid on 131 388, or Endeavour Energy on 131 003 or Essential Energy on 132 080, as shown on your power bill.

For emergency help in floods and storms, ring the SES (NSW and ACT) on 132 500.