Flash flooding that hit parts of NSW on Wednesday is unlikely to dry up on Thursday with the state to cop another drenching.

A low pressure system that hammered northern NSW is expected to move south to Sydney, the Illawarra, the Hunter and the Blue Mountains regions, continuing the long run of rainy days.

But the end is in sight for Sydney with the sun expected to finally peek through on Sunday.

"Today is probably the last of the significantly wet days in Sydney but we will still see quite a few showers on Friday and Saturday then, from Sunday, it will ease significantly," said Rob Sharpe, meteorologist from Weatherzone.

Thursday is expected to be largely dry for the Mid North Coast but rain will return on Friday through to Sunday with further flooding possible.

It will hamper efforts to clean up after the region received 100-200 millimetres of rain on Wednesday, causing flash flooding around Lismore, Grafton, Coffs Harbour, Port Macquarie and Taree.

Cape Byron received 162 millimetres, Port Macquarie received 166 millimetres and Coffs Harbour received 143 millimetres. 

Roads and ovals in Coffs Harbour turned into brown rivers and one resident captured video of a car submerged up to its roof in water off Hogbin Drive.

The State Emergency Service (SES) has had more than 1000 requests for help since yesterday and pleaded with people not to enter floodwaters.

The SES conducted 11 flood rescues including four overnight.

"Find another way to go around," said NSW SES spokesman, Wayne Snell. "It simply places you at risk, your passengers at risk and it also places our brilliant volunteers at risk when they have to come and rescue you."

Parts of western Sydney experienced flash flooding on Tuesday and flood rescues were undertaken in Erskine Park and Luddenham.

A childcare centre in Penrith was surrounded by flood, forcing the SES to evacuate 90 children.

The SES's Parramatta unit had to retrieve an abandoned car after it became trapped in floodwaters near Toongabbie.

A severe weather warning issued for the Mid North Coast on Thursday morning was later cancelled by the Bureau of Meteorology.

Weatherzone is owned by Fairfax Media