Large hailstones, heavy rainfall and damaging winds have been predicted during the storms which may affect  the Northern Rivers, Hunter, North West Slopes and Plains and parts of the Mid North Coast areas, as well as Central Tablelands, Central West Slopes and Plains, Upper Western and Northern Tablelands.

The warning was issued at 2:45 pm this afternoon and locations which may be affected are Lismore, Tenterfield, Newcastle, Scone, Cessnock, Maitland, Tamworth, Gunnedah, Moree, Narrabri, Walgett and Lightning Ridge. 

Authorities have warned the thunderstorms are likely to produce large hailstones, heavy rainfall that may lead to flash flooding and damaging winds in the warning area over the next several hours.

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 clear of fallen power lines. 

* Keep clear of creeks and storm drains.

 * Don't walk, ride your bike or drive through flood water. 

* If you are trapped by flash flooding, seek refuge in the highest available place and ring 000 if you need rescue. 

* 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.