The Bureau of Meteorology has issued a severe thunderstorm warning for Lismore and the Northern Rivers for damaging winds and large hailstones.

A trough combined with a warm and unstable airmass is triggering thunderstorms over the northeast today.

Severe thunderstorms are likely to produce damaging winds and large hailstones in the warning area over the next several hours. Locations which may be affected include Lismore, Casino, Kyogle, Coraki, Whiporie and Woodburn.

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 8 metres away from fallen power lines or objects that may be energised, such as fences.

* Report fallen power lines to either Ausgrid (131 388), Endeavour Energy (131 003), Essential Energy (132 080) or Evoenergy (131 093) as shown on your power bill.

* Trees that have been damaged by fire are likely to be more unstable and more likely to fall.

* Unplug computers and appliances.

* Avoid using the phone during the storm.

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

* Stay vigilant and monitor conditions. Note that the landscape may have changed following bushfires.

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

The next warning is due to be issued by 7:10 pm.

You can watch the weather radar through the Lismore App on the Weather/Travel button Weather & Travel.