UPDATE: 11am

The BOM has cancelled the severe weather warning for thunderstorms and heavy rain for the Northern Rivers.

The Bureau of Meteorology have said that severe thunderstorms are likely to produce heavy rainfall that may lead to flash flooding over the next several hours.

The affected locations which may be affected include Lismore and Alstonville as well as Tweed Heads, Murwillumbah, Byron Bay, Ballina and Brunswick Heads.

Lismore recorded 39mm at Lismore airport with 24mm falling on Wednesday.

The State Emergency Service advises that people should:

* 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.

* Be aware that run-off from rainfall in fire affected areas may behave differently and be more rapid. It may also contain debris such as ash, soil, trees and rocks.

* After bushfires, heavy rain and the loss of foliage can make the ground soft and heavy, leading to a greater chance of landslides.

* 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 update from the BOM is at 11am.