Sydneysiders' prayers for relief after days of intense heat were answered with flash flooding that caused chaos on the roads and left residents and travellers scrambling for help.

The sudden storm hit the city and surrounding suburbs yesterday leaving thousands of homes without power, a dozen people trapped in their cars in floodwaters and others stuck due to closed roads.

Light rail lines were suspended, flights were delayed and murder trials were interrupted when the Supreme Court building in the CBD was evacuated as water streamed down internal stairs.

The city was drenched by 35mm of rain in one hour between 10am and 11am local time as the storm cell hit.


The inner-city suburb of Marrickville bore the brunt of the deluge with 48mm of rain and a block of flats was at threat of collapsing, the SES said, with 100 people evacuated.

The SES responded to 126 calls for help, including at least 13 people trapped in their cars who had to be rescued in Leichhardt, Marrickville, Zetland and Alexandria.

Sydney's city streets were awash with pedestrians battling to walk through flooded crossings.

Light rail services were cancelled between Dulwich Hill and Central due to flooding. There were delays at Sydney Airport for both arrivals and departures and a small number of flights were cancelled while others were diverted.

More than 5100 properties were without power across Sydney.

A blackout in Redfern and parts of Surry Hills affected more than 700 homes and businesses, while 1400 properties were without power in Lane Cove, Ausgrid said.

Power provider Endeavour Energy said 1000 properties lost power in Ambarvale, with a further 2000 cut off throughout Sydney in suburbs including Kemps Creek and Riverstone.

Motorists travelling across the Anzac Bridge had to grapple with just one westbound lane for hours before the others were reopened in the afternoon.

While the worst of the storm has passed, Sydneysiders are being advised to keep their umbrellas in their bags with light to moderate rain forecast through to today.