The Bureau of Meteorology has issued a statement which says the storm is predicted to produce large hailstones and damaging winds over the next several hours.

Locations which may be affected include Port Macquarie, Taree, Newcastle, Gosford, Scone, Cessnock, Maitland, Armidale and Tenterfield.

The State Emergency Service advises that people should: 

* Move your car under cover or away from trees. 

* Secure or put away loose items around your house, yard and balcony. 

* Keep at least eight metres away from fallen power lines or objects that may be energised, such as fences. 

* Report fallen power lines to Essential Energy on 132 080, as shown on your power bill. 

* Unplug computers and appliances. 

* Avoid using the phone during the storm. 

* Stay indoors away from windows, and keep children and pets indoors as well. 

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