Cyclonic bomb: Sydney lashed with 'once in a century' storm

Sydney is cleaning up after what the Bureau of Meteorology is calling a 'once in a century storm'.

The damaging winds and extreme rainfall that tore through the city were caused by a low pressure system off the east coast of New South Wales that created several smaller low pressure systems, according to meteorologists.

Strathfield received 94 millimetres of rain in just three hours, which meteorologists say is a once in a century event.

Seven meteorologist David Brown said the storm was "a classic cyclonic bomb".

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"There’s no doubt that is was a powerful storm, in fact it packed as much punch as a category two tropical cyclone," he said.

The highest reported wind was 161km/hr at Wattamolla, just south of Sydney little after nine in the evening, Brown explained.

"Delving through the records, a storm of a similar intensity hammered the Hunter coast in May 1974 - gusts to 165km/hr were recorded at Newcastle's Nobby's Head."

"Last night’s storm was a classic cyclonic bomb that unleashed storm force winds along the Illawarra and Central coasts for several hours.

The rapid development of the low pressure system lead to the flooding rains and destructive winds.

"There is no doubt there’ll be more east coast lows over the coming months, but it’s highly unlikely they’ll pack as much power as last night."

A massive clean-up is underway and travel plans have been thrown into disarray, after a destructive storm lashed the New South Wales east coast overnight. Photo: AAP

The raging weather blanketed the Blue Mountains in snow, stranded motorists in floodwaters in Sydney, and left thousands of homes without power.

It comes as many Blue Mountains residents are still grappling with blown-out rebuild costs after losing their homes in last year's catastrophic bushfires.

A busy night for emergency services with swift water rescues and flood evacuations. Photo: SES

Gallery: Extraordinary photos from the storm that hit NSW overnight. Photo: 7News viewer Sarah Rich

The massive storm tore through NSW's east coast, battering homes and causing delays at Sydney Airport.

Ferocious winds of up to 160km per hour, equivalent to a category two cyclone, coupled with torrential rain and snowfall resulted in more than 1200 emergency calls for help in NSW as storms tore across the state's east coast.

The NSW SES reported unseasonally heavy snowfall of up to 20cm in parts of the Blue Mountains including Lithgow. A warning was issued for people to avoid the area due to snow causing branches to fall on cars and also local roads closures.

There are reports one family needed to be rescued after becoming trapped in their car by a fallen tree.

Sydney train stations including Bardwell Park station were flooded by the intense downfall and flash floods. Photo: Nikkiarief via Instagram

More than 30,000 people in metropolitan Sydney, the Blue Mountains, Southern Highlands and the Illawarra regions were without power on Tuesday night and Wednesday morning as strong winds brought down powerlines.

State Emergency Services cleared 600 jobs, saying the severe conditions prevented access to some homes.

Snowfall in the Blue Mountains left people stranded on roads, and an aged care facility without power.

SES warns commuters of public transport delays on Wednesday, with Parrammatta Station in Sydney's inner west flooded.

Fifty passengers on a train stranded by flooding at North Bexley Train Station in Sydney's south.

Flash flooding across the state prompted at least 57 rescues, with many people being trapped in cars after driving into floodwaters.

Six people were helped from a building in Allawah in after a retaining wall collapsed.

The storm is expected to move north on Wednesday towards the Hunter Region and Central Coast.

Lightning strikes lit up skies during the severe storm. Photo: Getty

The Bureau of Meteorology is forecasting damaging to destructive winds around 80km/hr with peak gusts of 125km/hr on the coast fringe.

Expected heavy rain could lead to flash flooding in parts of the Hunter.

Very heavy surf conditions are also forecast for the metropolitan, Hunter and Illawarra areas.

Overnight, Fire and Rescue NSW dealt with two reports of lightning strikes on houses, one of which caused a large fire at a Kellyville two-storey home, but no one was reported hurt.

A dog waited at Bronte Beach as the severe storm hit Sydney earlier in the week. Photo: Getty

The State Emergency Service said that by 4am on Wednesday it had received 1230 requests for help, mainly from the Illawarra, the south coast and south and southwest Sydney.

Sydney Airport was hit by wind gusts of up to 106km/h, which will likely result in delays for passengers on Wednesday.

"Flights are coming in and out, the weather is causing delays to unloading aircrafts... it will contribute to knock-on delays," an airport spokesperson said.

Gusts of 161km/h were recorded at Wattamolla in the Royal National Park, and 115km/h at Kurnell, and high winds were continuing along the coastal fringe of the Illawarra and Sydney early on Wednesday.

The sky above Bronte Beach was blanketed in thick cloud as the storm hit. Photo: Getty

NSW's south coast has been hit by the heaviest rainfall, with 170mm falling at Lake Conjola and 145mm at Ulladulla.

Sydney has also been drenched, with falls of 136mm at Sans Souci, 118 at Marrickville, 114 at Peakhurst and 113 at Strathfield.

Heavy snow fell in the Blue Mountains including Lithgow, with reports of up to 20cm in some places. Photo: NSW SES

Thousands of homes in Sydney's south have experienced power cuts, including in Bexley, Bankstown and Blakehurst.

The storm was trending strongly on Twitter, with disgruntled passengers venting anger about delays at the airport and NSW residents posting pictures of damage.

Bexley Road in Sydney's south was closed due to heavy flooding. Photo: NSW SES