Seven more natural disaster areas in Australia's New South Wales (NSW) were declared on Friday as the worst flooding in years shows no signs of letting up over Christmas.

The newly declared seven natural disaster zones are in the state's southwest and in the central west.

There are now 49 natural disaster areas in NSW, each qualifying for commonwealth and state cash.

Heavy rain that caused the flooding has cleared from most parts of the state, but the lower reaches of many inland rivers continue to rise, swamping roads and isolating communities.

The State Emergency Service (SES), which has carried out 150 rescues since the flooding began in late November, said it is well placed to continue helping communities over Christmas.

"This will continue over the holiday period with the SES ready to assist should further heavy rain or storms occur," SES commissioner Murray Kear said in a statement.