Heavy rain across much of NSW is "breaking the back" of the state's horror bushfire season but also keeping emergency services busy with flooding along the coast.
The Bureau of Meteorology warns torrential rain of up to 200mm is possible overnight in the state's central coastal area including greater Sydney, the Central Coast, Illawarra, Southern Highlands and Blue Mountains.
This could cause "potentially life-threatening" flash flooding and commuters are advised to delay non-essential travel in those areas, the bureau says.
Up to 300 millimetres has been recorded in some parts of the north coast with similar totals expected in the Sydney basin by the end of the weekend.
Severe weather caused havoc for Sydney's train network on Friday night, temporarily damaging signal equipment at Lidcombe and delaying some services by more than 90 minutes.
The equipment has been repaired but Transport for NSW advised commuters to keep allowing extra travel time as major delays continued.
BOM acting NSW manager Jane Golding says rain could cause roads to be flooded in the city, but much less will fall in the state's drought-ravaged west.
"The bulk of the rain does look like it will affect the coastal ranges and the eastern side of the divide," Ms Golding told reporters on Friday.
The NSW State Emergency Service has responded to 683 jobs across the state since the wet weather arrived on Wednesday.
In the northern rivers region, a car was washed off a road in Glenreagh, and in Tyagarah two people had to be rescued from a caravan due to rising floodwaters.
"Most of the damage so far is the leaking roofs, damaged properties, fallen trees and stranded motorists, some of whom have attempted to drive through flooded areas," SES commissioner Carlene York said on Friday.
The SES will be moving resources down into the Illawarra and the South Coast over the weekend as the weather system moves south.
"The fire damaged areas will bring extra risks as the heavy water and floods move through (with) more likelihood of fallen trees and more run-off," Ms York said.
NSW Rural Fire Service commissioner Shane Fitzsimmons says the rain is "breaking the back" of the horror bushfire season.
"The rain is good for business and farms as well as being really good for quenching some of these fires we've been dealing with for many, many months," the commissioner told ABC TV on Friday.
"We don't want to see lots of widespread damage and disruption from flooding, but it is certainly a welcome change to the relentless campaign of hot, dry weather."
There are currently 38 fires burning across NSW.
The Bureau of Meteorology on Friday issued a severe weather warning for heavy rainfall, damaging winds, abnormally high tides and damaging surf, stretching along the coast from the Northern Rivers to South Coast regions.
Water overflows the banks of the Parramatta River after heavy rains buffeted Sydney. Source: AAP
Hazardous surf warnings are also in place for the Macquarie coast, Hunter coast, Sydney coast, Illawarra coast, Batemans coast and Eden coast.
Wind warnings have been issued for the Hunter coast, Macquarie coast, Sydney coast and Ilawarra coast, while minor flood warnings are in place for the Bellinger, Kalang, Orara and Paroo rivers.
Soggy streets greated commuters as they travelled through inner-Sydney. Source: AAP
Parts of the North West Slopes and Plains and Northern Tablelands regions are also subject to a severe thunderstorm warning.
Overjoyed residents welcome rain
Videos and photos of heavy rain falling have been posted online by residents.
One resident said the deluge was enough to fill their rainwater tank "10 times over".
