Southern Sydney resembled a disaster zone on Wednesday after the most destructive winds recorded in NSW history lifted roofs off houses, brought down power lines and trees and left more than 20,000 homes and businesses without power.

The first of multiple severe thunderstorms hit Sydney just after 10:30am, when a tornado-like event ripped through the Sutherland shire region.

The storm's brunt was felt in southern beachside suburb of Kurnell, which was lashed with record breaking winds of 213km/h, heavy rain and golf-ball sized hail. A trail of destruction confronted residents and State Emergency Service workers on Wednesday afternoon as they worked to remove debris and cut down trees that had fallen across roads, yards and cars.

Several homes lost their roofs and power was cut to 800 residents and 7000 businesses, as metal sheeting was strewn across roads and roof tiles ripped off and thrown into adjoining properties.

Large hail stones currently hitting North Cronulla Beach right now. Photo: Luke Calo. #9News pic.twitter.com/TKKEA9r0WU— Nine News Sydney (@9NewsSyd) December 15, 2015

Two men were also taken to Sutherland Hospital after a roof collapse at an industrial unit complex on Sir Joseph Banks Drive. Dozens more residents still had not returned to their homes late on Wednesday afternoon and remained at an emergency evacuation point at the Cronulla Leagues Club.

Wind gusts of up to 213km/h, which hit Kurnell and Cronulla just before 11am, set a new record for NSW. The previous wind gust record was 171 km/h, recorded at Newcastle's Nobby's Signal Station on May 26 1974.

"There is obvious evidence that we have had a tornado go through Cronulla today," said Alan Sharp, a meteorologist at the Bureau of Meteorology.

James Taylor, senior meteorologist at the bureau's extreme weather desk, said he could not believe the strength of the winds.

"I was astounded to see that the automatic weather station was able to record that wind gust and not fail under the onslaught it would have been copping."

Around 1:30pm another series of thunderstorms struck Sydney city and the eastern suburbs, causing flash flooding and damaging buildings. Shoppers were evacuated from Bondi Junction Westfield and a woman was taken to St Vincent's hospital with head and elbow injuries after a section of the shopping centre's roof collapsed.

Westfield RT @9NewsSyd: Part of the roof at Bondi Junction has fallen in due to heavy rain. Pic: @laurencro #9News pic.twitter.com/R8kr8qauCz— Rick Eyre (@rickeyre) December 16, 2015

By 6.30pm on Wednesday SES teams had responded to roughly 600 call-outs to parts of southern Sydney, as well as Bondi, Bellevue Hill, Maroubra and Port Botany.

"There is a lot of roof damage, trees down, power lines down. And in Sydney's east it has been mostly incidents of flash flooding," said Sue Pritchard, SES spokesperson.

Ms Pritchard said calls were expected to peak as the working day came to a close and people returned home to damaged property.

SES volunteers had also made 15 flood rescues by Wednesday afternoon, all of which involved people who were trapped in their vehicles after driving into flood waters.

Commuters also experienced chaos on the roads, with flooding, power failures, car crashes and fallen trees causing havoc across the city.

Traffic banked up as major roads, including Syd Einfeld Drive at Bondi Junction, Alison Road at Randwick and Captain Cook Drive in Cronulla, were either completely or partially shut.

Flights out of Sydney's airport were grounded during the midday storm, causing delays for commuters travelling out of Sydney, while incoming flights were diverted to airports elsewhere in Australia.

.@guardianaus reader Claire Milet took this, of people getting out of cars to walk to #SydneyAirport in #sydneystorm pic.twitter.com/7GbkszdJcp— (Joyeux No)Elle Hunt (@mlle_elle) December 16, 2015

Fed up passengers abandoned their cars amid heavy traffic, and ran with their luggage towards the airport.

SES volunteers expected the clean-up from Wednesday's storm to continue into the end of the week.

"Remember, our people are volunteers. So at the end of the day when they finish work they'll be putting their orange outfits on and heading out to work again. We imagine the work will go into Thursday," Ms Pritchard said.

with Melanie Kembrey, Marcus Strom, Emma Partridge, Ava Benny-Morrison