UPDATE: NORTHERN NSW residents who were hit with wild weather in the wake of Cyclone Oswald are preparing for a fresh deluge.

The Bureau of Meteorology has issued a flood watch for a huge swathe of the state, stretching from the Queensland border to the Hunter Valley north of Sydney.

A tropical low pressure system is likely to bring localised flash flooding and moderate to major river flooding, the BoM said, warning that some areas could expect rainfall of more than 300mm over today and tomorrow.

A severe weather warning for damaging winds and heavy rain was issued for the northern rivers, mid-north coast and northern tablelands districts this morning.

Residents in Lismore, Grafton, Bellinger, Coffs Harbour, Woolgoolga, Sawtell and Dorrigo may all be in the path of the low.

The State Emergency Service has already rescued two people who became stranded in their home at Lismore, and assisted with an emergency medical evacuation at Mullumbimby.

Some of the towns on flood watch are still mopping up after wild weather hit NSW over the Australia Day long weekend, causing millions of dollars in damage.

There were more than 50 flood rescues then, mostly of people who had driven into floodwaters.

"It is pretty much groundhog day for us, it's the same areas that are in the danger zone," a SES spokeswoman told AAP.

Residents on flood watch are urged to tie down their outdoor furniture, clean their gutters and urged not to drive in floodwaters.