Severe thunderstorms are likely to produce heavy rainfall that may lead to flash flooding in parts of the northern rivers over the next several hours.
A warning issued by the Bureau of Meteorology at 10.27am said locations that may be affected include Lismore, Ballina, Coraki, Alstonville, Evans Head and Woodburn.
The bureau reported that 54.2mm of rain as recorded at Yamba between in an hour 4am and 5am this morning.
The State Emergency Service advises that people should keep clear of creeks and storm drains and avoid walking, riding or driving through flood water.
If you are trapped by flash flooding, seek refuge in the highest available place and ring 000 if you need rescue.
People are also advised to unplug computers and appliances, avoid using landline phones 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.