A teenage boy, and a State Emergency Service volunteer were killed as a massive storm dumped a month's worth of rain on Sydney in just hours yesterday, bringing down trees and powerlines, flooding homes and bringing the city to a standstill.

A third person, yet to be identified, died when their car crashed into a powerpole on Old Prospect Rd at South Wentworthville about 7pm.

The driver died at the scene, while a passenger in the car was uninjured

The 14-year-old was killed during the morning commute when the Toyota Corolla his 17-year-old brother was driving on P-plates collided with another car on The Esplanade in Thornleigh on the city's upper north shore. The pair lived a short distance away at Westleigh.

Residents said the crash sounded like thunder.

"It is just this horrible spot where it is an accident waiting to happen," one said.

"It is so narrow … and there is so many entry streets where people take risks to cross both lanes."

 

The Landrover at the scene of the fatal car accident on The Esplanade at Thornleigh. Picture: AAP
The Landrover at the scene of the fatal car accident on The Esplanade at Thornleigh. Picture: AAP

 

The Toyota Corolla ploughed into parked cars after the collision with the Landrover. Picture: AAP
The Toyota Corolla ploughed into parked cars after the collision with the Landrover. Picture: AAP

While in the Shoalhaven a male SES volunteer aged in his 40s collapsed and died while assisting with the floods. It is believed he suffered a heart attack.

Across the state the deluge wreaked havoc with Sydney Airport reduced to a single runway and 150 flights cancelled, roads closed and the State Emergency Service responding to 800 requests for help and 16 flood rescues before midday.

The Macquarie St exit of St James station flooded. Picture: John Grainger
The Macquarie St exit of St James station flooded. Picture: John Grainger

As the weather system moved north on Wednesday night the SES was dealing with 1700 jobs after receiving 2300 calls for help across NSW.

Two police officers helping motorists stuck in floodwaters at North Ryde were struck by a falling 40 metre gum tree as they pushed a trapped car.

A massive gum tree and power lines blocked Eastern Valley Way at Castle Cove. Picture: Twitter/Live Traffic Sydney
A massive gum tree and power lines blocked Eastern Valley Way at Castle Cove. Picture: Twitter/Live Traffic Sydney
A Jacaranda tree brought down powerlines in McCabe Place in Chatswood.
A Jacaranda tree brought down powerlines in McCabe Place in Chatswood.

 

A female officer suffered a suspected broken leg and a male officer was concussed.

The officers were helping Zac Morris when the tree hit. He managed to climb out through his window.

"I literally heard the noise and the roof just sort of craved in," he said.

Anthony Ho was one of those rescued from his car after it became trapped in flood waters.

"It was a bit deep. It was getting a bit deeper what I would have expected," he said.

A car crushes by a tree in Marion St at Leichhardt. Picture: Twitter/@divingdingo
A car crushes by a tree in Marion St at Leichhardt. Picture: Twitter/@divingdingo

In Chatswood 70km/h winds ripped the walls and windows from an office building.

"I started to go upstairs to see if there was any damage and next minute there was an almighty bang and it ripped panels off the roof in the warehouse," Greg Transell told the ABC.

"It's sucked some of the doors the reverse way out through the frames and actually dislodged the frames and all the rubber lining that holds the windows."

 

Cars navigate the floods at Glebe.
Cars navigate the floods at Glebe.

 

Two cars became stuck on the ramp to the M2 at Ryde. Picture: 9 News
Two cars became stuck on the ramp to the M2 at Ryde. Picture: 9 News

 

Sydneysiders woke to drumming rain and rolling thunder after 6am. Observatory Hill in Sydney recorded more than 118mm in the six hours to 11am - dwarfing the 83.8mm average rainfall for the entire month of November.

Bureau of Meteorology state manager Ann Farrell said: "For that intensity and that duration, that's the sort of rainfall you'd expect to occur about once every hundred years for that particular site."

The north shore copped the worst of the rain with 140mm falling at Mosman.

The Gleeson home at Cammeray flooded.

"There was this ton of water coming down and sort of went through our house to the backyard, broke our neighbours fence on the right side. Just this massive river," Billy Gleeson told Channel 10.

The Gleeson family woke to find their entire back yard, living room and kitchen flooded on Wednesday morning in Cammeray. Picture: Facebook
The Gleeson family woke to find their entire back yard, living room and kitchen flooded on Wednesday morning in Cammeray. Picture: Facebook
Billy Gleeson is interviewed by Channel 10 on Wednesday. Picture: Facebook
Billy Gleeson is interviewed by Channel 10 on Wednesday. Picture: Facebook

In Chatswood 119mm fell while Shoalhaven's Porters Creek Dam received 168mm.

The chaos continued into the afternoon with high winds and warnings for commuters to begin the soggy trip home early.

Buses, trains the light rail and ferries were all affected.

The flashing rain overwhelmed stormwater drains, closing the Anzac Bridge and roads in Rozelle, North Narrabeen, Oxford Falls and Annangrove.

A landslide caused lengthy traffic delays along the Great Western Highway near Macquarie Road in Springwood in the Blue Mountains.

Acting Superintendent Steve Vaughan from NSW Ambulance said: "Between 6am and 12pm NSW paramedics attended 47 motor vehicle accidents, 33 in Sydney itself."

By 6pm there had been 83 crashes, 10 an hour, with 20 people hospitalised.

The call-outs were four times the daily average and he said at times the rain was so intense the rescue helicopters were grounded.