'Worst is yet to come' for NSW floods, Australia

The Australian government has declared a natural disaster in large swaths of New South Wales (NSW), as heavy rains batter the state and force thousands to evacuate.

Rains have been inundating communities since Thursday.

More than 15,000 people have been evacuated from the Mid-North Coast and more than 3000 across the Nepean and Hawksbury area.

Minister for Police and Emergency Services, David Elliott said he had signed 16 disaster declarations for parts of NSW to get assistance to them as soon as possible.

NSW Premier Gladys Berejiklian urged residents to follow local guidance, stay off the roads, and heed evacuation orders if needed.

"This is nothing like we've seen since the 1960s," she said.

"We're not through the worst of it yet and that's why we need to brace ourselves."

Since Thursday, the State Emergency Service (SES) has responded to 8,000 calls for assistance.

Authorities don't know yet how many homes or infrastructure have been lost, but "the damage is substantial," Berejiklian added.

The Australian Government Disaster Recovery Payment (AGDRP) and Disaster Recovery Allowance (DRA) has been activated to support those heavily affected by the storms and flooding, Prime Minister Scott Morrison announced in a Facebook post on Sunday.

"The terrible storms and floods that have been ravaging NSW for the past few days are taking a heavy toll," Morrison said in a video address.

The PM also praised emergency workers and volunteers, urging people in flood-hit regions to listen to their advice and warnings, saying "for now, our message is very clear to keep yourself safe, to keep your family safe and those around you to follow the instructions of the very competent, professional agencies and bodies and the volunteers who support them."

Wednesday will be the first day of some reprieve, with rains expected to lighten into showers.

Our thoughts go out to all those affected by the terrible floods in NSW.