A nasty thunderstorm has wreaked havoc across Sydney, with damaging hailstones, raging winds and flooding from the torrential rain.

Hailstones fell in numerous parts of Sydney, including Pymble where it blanketed grass in the area in white.

Hail looks like carpet of snow in Pymble. #SydneyStorm @702sydney @abcnews pic.twitter.com/e5Da8oHEJn — Elysse Morgan (@ElysseMorgan) December 7, 2014

The storm washed across the western suburbs of Sydney just after 4pm, rolled across the city about 5.30pm and was expected to push out to sea by 6pm.

Tropfest, the world's largest short film festival, has recommenced after the site was earlier closed down due to lightning strikes.

The State Emergency Services was receiving 10 calls per minute after the storm struck on Sunday afternoon. The main areas hit included Ku-ring-gai, the Hawkesbury, Warringah and Camden.

#longreef RT Good afternoon tweeps! We'd love to see your storm pics -tweet us at @smh or #sydneyweather #SydneyStorm pic.twitter.com/bE6nWsCE8Z — Warringah (@warringah) December 7, 2014

About 5pm they responded to an alert for a person trapped in a car at a four car pile-up on Windsor Road at Vineyard.

Between 2.30pm and 5pm, Fire and Rescue NSW responded to more than 80 storm-related callouts, mostly from Sydney's northern suburbs. At Winston Hills a house was on fire due to a lightning strike.

CareFlight said a man at Bligh Park was trapped under an awning that collapsed when hit by a tree. He has been transferred to Westmead Hospital in a serious but stable condition.

UPDATE: A man has been freed after a tree fell on to a pergola at Bligh Park. More in #9NewsAt6 pic.twitter.com/M67KjsBxNW — Nine News Sydney (@9NewsSyd) December 7, 2014

Sydney's lord mayor Clover Moore said the Surry Hills Christmas concert had been cancelled due to the storm.

Unfortunately, because of the storms, tonight's Surry Hills #sydxmas concert has been cancelled. — Clover Moore (@CloverMoore) December 7, 2014

An afternoon race at the V8 Supercars Sydney 500 event was also abandoned.

Michael Logan, a forecaster for the Bureau of Meteorology, said areas in Sydney's north and west were worst affected. Some areas received up to 30 millimetres of rain in 20 to 30 minutes.

Hailstones fell in numerous parts of Sydney, including Pymble where it blanketed grass in the area in white.

Hail looks like carpet of snow in Pymble. #SydneyStorm @702sydney @abcnews pic.twitter.com/e5Da8oHEJn — Elysse Morgan (@ElysseMorgan) December 7, 2014

Transport Management Centre said the wet weather had blacked out traffic signals and brought down power lines across Sydney.

@smh at Bondi an hour or two ago. pic.twitter.com/vCCLdhkwfp — Anita (@xXEvilMidgetXx) December 7, 2014

There were several sets of traffic signals blacked out across Sydney including at Hornsby, Harbord, Mona Vale, Rosehill and Rouse Hill.

There were fallen trees and downed power lines at Londonderry, Vineyard and Glenorie.

The bureau's severe weather meteorologist Andrew Haigh said wind gusts of 101 and 90 kilometres per hour were recorded at Mudgee and Camden Airports respectively.

The thunderstorms were detected on weather radar at 12:45pm and were expected to lash the affected areas for at least a couple of hours.

The storm was expected to break after 6pm but there was a chance of further thunderstorms into the evening and bureau could not rule out them becoming severe.

Just fled a hailstorm. The day an actual apocalypse comes I'll be prepared. #SydneyStorm pic.twitter.com/LTTX5Rl6ym — Rachel Avison (@rachelanne89) December 7, 2014

Earlier, the bureau recommended affected residents should move cars under cover away from trees, secure any loose items, keep clear of fallen power lines, avoid using the phone during the storms and to call the State Emergency Service on 132 500 for any emergencies.

Storm warnings are available through TV and Radio broadcasts, the Bureau's website at www.bom.gov.au or call 1300 659 218.