A Woolworths and local motel have been flooded and the roof of an aged care facility has partially collapsed after an intense cloudburst in central-western New South Wales.
Parkes received 31mm of rain in just 17 minutes during the Saturday afternoon downpour.
By Sunday morning the town had recorded 52 millimetres in total. The storm also brought damaging winds and large hailstones.
Part of another roof blew off, and residential properties also experienced flooding.
Thunderstorms across much of NSW prompted 45 calls for assistance between 6 p.m. Saturday and 6 a.m. Sunday, the State Emergency Service said.
Broken Hill and Parkes have been hardest hit by the extreme weather over the past few days, with Wauchope and Taree on the mid-north coast also affected.
The biggest downpour on Saturday was at Okeh to the north, which copped more than 61mm to 9 a.m. Saturday.
The SES has responded to 300 incidents statewide since New Year's Eve, including four flood rescues.
Near Parkes, a person was trapped in a car in floodwater.
A driver and passengers were stranded in their vehicle in Tibooburra, in the state's west, on New Year's Eve, while at Wauchope, on the mid-north coast, two people had to be rescued from rising waters late on Friday.
Persistent unpredictable bad weather had caused dangerous flash flooding around the mid north coast, closing bridges and roads, Ilana Pender-Rose of the SES told AAP on Sunday morning.
About 1,640 residents remain circled by water and cut off in Taree, Harrington and Camden Haven.
Some are expected to be isolated for weeks, others for only a few days.
Flood alerts are current for the Bellinger, Hastings, Paroo and Camden Haven rivers.
The wet weather has been caused by an inland trough with upper-level system support, Shuang Wang of the Bureau of Meteorology said.
Rainfall will continue throughout the state as the trough moves east, with possible thunderstorms on Sunday afternoon.
Monday "will be a big day" across the most eastern part of the state, potentially affecting Sydney and Canberra, Wang said.
"We're asking people to get ready because this probably isn't over," Pender-Rose said.
She asked people to be aware of flood risks as they return from holidays around NSW but especially on the mid-north coast, where SES volunteers have set up sandbagging stations.
"Please take it easy, think before you drive anywhere and be aware of the flood risk of wherever you are staying," she said.
Sydney is also set for a rainy few days. There's a very high chance of rain until Tuesday, with a good chance of showers beyond that.
Swimmers have been warned to avoid Bronte beach and Narrabeen Lagoon because of pollution caused by rain. Many other swimming sites throughout the city and the Illawarra are also affected.