Natural disaster declared in Aus state, evacuations on

Flooding in parts of New South Wales (NSW) was declared a natural disaster on Sunday and residents in flood-hit areas west of Sydney were evacuated as Australia's most populous state continued to be hammered by heavy rain.

Sixteen areas, primarily in the north of the state, were declared "disaster ridden", dpa news agency quoted NSW Police and Emergency Services Minister David Elliott as saying at a press conference.

"Regrettably, parts of the mid-north coast are experiencing a one in 100 years event," NSW Premier Gladys Berejiklian told journalists.

Parts of Port Macquarie, some 400 km north of Sydney, and several nearby towns flooded, while further south Taree was in the grip of a flood rivalling its worst on record 92 years ago.

In nearby Mondrook, a three-bedroom cottage was swept away from its foundation by floodwater in footage shown on local television over the weekend.

The Premier said that, however, the area of major concern was the Nepean Valley, incorporating major urban centre Penrith, part of Greater Western Sydney, where local authorities were "envisaging a one in 50 years event".

The NSW Bureau of Meteorology (BoM) said in a Sunday warning that the Nepean Valley was set to experience its worst flooding in 50 years as the Warragamba Dam, Sydney's main water source, began spilling on Saturday afternoon causing river levels to rise along the Nepean and Hawkesbury rivers.

Berejiklian warned that, after a number of residents in flood-hit areas were already evacuated on Saturday night, a further 4,000 people in the "Hawkesbury region and parts of western Sydney" may be next.

On Saturday night, the NSW State Emergency Service (SES) ordered anyone in low lying areas of Agnes Banks, Pitt Town Bottoms, Pitt Town North, Cornwallis, Gronos Point and North Richmond, some 50 km west of Sydney on the Hawkesbury river, to evacuate.

The BoM on Sunday morning warned of further heavy rainfall and damaging winds, with a severe weather warning covering almost 900 km of coast from Wollongong, south of Sydney, to Lismore near the border with Queensland.

A severe weather warning was also in place just west of Canberra.

Meanwhile NSW police said two hikers who on Saturday remained "stuck between two large bodies of water" in the Blue Mountains, west of Sydney, were among the over 670 people rescued since the severe weather event started on Friday.

Police were also looking for a bodyboarder believed to be "missing in waters" at Coffs Harbour, some 430 km north of Sydney.

So far there are no reports of deaths.

The heavy rain is expected until Thursday, according to the latest forecast.