The bureau issued the warning shortly after 4pm and say Tamworth, Gunnedah, Moree and Narrabri could be affected.

Severe thunderstorms are likely to produce damaging winds in the area over the next few hours with large hail and heavy rain that may lead to flash flooding also possible over the Northwest Slopes and Plains and Upper Hunter. 

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. 

* 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. 

For the latest updates visit bom.gov.au