UPDATE: ABOUT 2000 people have been cut off by floodwaters, as destructive winds and rain hit northern NSW and move slowly south.

Severe weather warnings have been issued for much of NSW as ex-tropical cyclone Oswald currently moves slowly across the Queensland border, ushering in winds of up to 140km/h.

People in Sydney, the Illawarra, the Northern Rivers, the mid-north coast, the Hunter and the northern and central tablelands are all being warned to prepare for heavy rain that may lead to flash flooding, with the Hopkins Creek weather station near Mullumbimby on the far north coast recording almost 540mm of rain in the last 24 hours to 9am.

Bureau of Meteorology forecaster Mohammed Nabi said the wild weather was expected to reach east of Moree this afternoon, and west of Armidale this evening.

He said the low-pressure system, which has lost its structure since being a Category 1 cyclone, was dumping a lot of moisture from the Tasman Sea on coastal areas.

As it moves south, he said Sydney Newcastle will probably start seeing the worst of it on late Monday evening with winds forecast to reach up to 100km/h and downpours of up to 200mm.