Thunderstorms struck NSW during peak hour on Wednesday, bringing large hailstones, damaging winds and heavy rain.

A severe thunderstorm warning for Sydney, the Illawarra, Hunter, mid-north coast and upper western and northern tablelands was cancelled after storms swept through the state.

The storm led to flash flooding and damaging winds.

• Wild weather brings Melbourne to a standstill

A woman in her 30s in western Sydney was struck by lightning outside a primary school. An ambulance spokesman said she was treated for shock and minor burns.

Lightning also took out train signals in the western suburb of Granville.

Around 17,000 homes and businesses across Sydney’s west are without power.

Endeavour Energy said electricity supplies have been cut to 9,000 customers at Minto, Eagle Vale, Fairfield, Prestons and Moorebank.

Nearly 8,000 more homes are without power around Wentworthville, Toongabbie, Emu Plains, Richmond and Kenthurst.

It has all gone to pot in Sydney with storm causing chaos throughout the region #sydneystorm http://t.co/NGOUC11Tqi pic.twitter.com/YO8LiXIqYq

— Matt Cullen (@Mattcullen1976) November 5, 2014

Bureau of Meteorology spokesman Derryn Griffiths said most of Sydney would be hit over the next couple of hours.

“There’s a storm north of Hornsby moving towards Mona Vale, it’s looking particularly dangerous, the strongest storm that’s currently showing on the radar,” she said.

“But the rest of Sydney is likely to get storms going over them some time this afternoon or evening.”

At Sydney Airport, planes were delayed for nearly an hour after winds of 60km/h lashed the tarmac.

Fire and Rescue New South Wales tweeted that crews were attending to storm incidents, including several accidents, wires down, trees down, flooding and an electrical fire.

The State Emergency Service (SES) has so far received 70 calls for help.