The weather bureau says northeast NSW is in for several hours of severe storms that may bring flash flooding and strong winds.
The Bureau of Meteorology says the storms will hit the Northern Rivers, Mid North Coast, North West Slopes and Plains, Northern Tablelands and parts of the Hunter.
It says the area may experience large hailstones, heavy rain that may lead to flash flooding, and strong damaging winds during the next several hours.
Locations that may be affected include Lismore, Grafton, Coffs Harbour, Port Macquarie, Taree, Armidale, Tamworth and Moree.
The State Emergency Service is advising residents to take all precautions including moving their cars under cover or away from trees, securing or putting away loose items around the house, and staying clear of creeks and storm drains.
Queensland has also been warned of possible further storm activity today as people in the Brisbane begin assessing the damage caused by severe thunderstorms yesterday.
Powerlines were ripped down, trees were uprooted, roofs collapsed and a fire started, as the thunderstorms ripped across the state overnight causing mass electricity outages.
More than 11,000 lightning strikes were recorded across Queensland's southeast since 10am (AEST) Saturday, with Energex receiving reports of more than 100 powerlines down.