More than 16,000 Sydney homes and businesses are preparing to spend a night without power after a severe storm ripped through the city bringing trees crashing down on power lines, houses and cars.
Trains and flights were delayed while commuters heading home experienced traffic chaos on Wednesday afternoon with damaging winds and heavy rain.
Residents in Mount Druitt and the Hills District were the worst hit with lightning and strong winds cutting power to 33,000 properties at the peak of the storm late Wednesday afternoon.
By the evening, power was restored to around 17,000 properties but just over 16,000 were still without electricity, an Endeavour Energy spokesman told AAP.
Residents in Mount Druitt, Castle Hill and Penrith will remain without power overnight and into Thursday with additional crews brought into the storm-affected area to help clean up and repair work.
In Sydney's north 800 homes in Berowra were under a blackout while 1300 were in the dark in the Central Coast suburbs of Woy Woy and 400 in Saratoga.
But those residents can expect to have power back up by midnight, an Ausgrid spokeswoman told AAP.
The NSW SES received 418 calls for help mostly in western Sydney with several reports of trees falling on roofs and cars.
"It's been quite a quick, fast, intense storm that's come," SES spokeswoman Becky Gollings said.
A child who was reported missing in floodwaters in the western Sydney suburb of Shalvey was safely pulled from the water by friends.
Train commuters to the Central Coast were left stranded with cancelled services while Blue Mountains travellers were delayed by 20 minutes.
In St Marys, lanes in the Great Western Highway were closed after a tree fell onto power lines.
The storm dumped up to 20mm in just a matter of minutes in some suburbs. Baulkham Hills was pelted with 27mm in 15 minutes.
The storms are expected to move over the city on Wednesday evening after unstable conditions persisted throughout the day.
Wind gusts reached 85km/h at Cowra in the central west and Goulburn in the southern tablelands.
The Bureau of Meteorology said even stronger gusts could be recorded in Sydney.
Conditions should settle by the end of the week, however, with only a few showers expected on Thursday and Friday.