Sydney soaked as storms set to continue

Sydneysiders are dealing with traffic chaos as residents along the length of the NSW coast are being told to prepare for heavy rainfall, damaging winds and large hailstones.

A severe thunderstorm warning has been issued for the state's east with damaging winds up to 90km/h possible including in Sydney, the Hunter region and the Blue Mountains.

Dungong in the Hunter region received 40 millimetres in just 30 minutes during the afternoon as heavy rains drenched much of NSW.

In Sydney, the stormy conditions combined with a car crash on the Harbour Bridge led to peak-hour gridlock with lengthy delays on major arterial roads.

Southbound traffic was queued back into the Lane Cove Tunnel while northbound traffic stretched over the Anzac Bridge to Rozelle, the Transport Management Centre said in a statement. Buses were delayed up to 30 minutes.

Elsewhere flooding caused road closures and trains were cancelled due to the severe weather.

Northern lines trains were "bumper to bumper" between Milsons Point and Central, one guard said, after lightning strikes caused delays.

The storm front initially moved across parts of Wollongong, Sydney and Newcastle early on Thursday evening.

Emergency crews worked through the night to restore power to more than 40,000 homes.

Some 470 homes remained without power on Friday evening mostly in and around Warragamba and Silverdale.

The State Emergency Service received 1700 calls for help across NSW and responded to 866 jobs with leaking roofs and downed trees the most common issues.

The SES had to rescue three people from flooded cars in Sydney and four in Albury.

A spokesman warned motorists to avoid unnecessary travel on the weekend and to be vigilant on the roads.

Lightning strikes affected flights at Sydney Airport with 30 domestic flights delayed or cancelled by 5pm on Friday.

The Bureau of Meteorology says Sydney could experience severe thunderstorms again on Saturday.

There's a 95 per cent chance of rain, the bureau forecasts.