Sydney storms leave teen dead

A teenager has been killed after being struck by lightning.

A teenage boy is dead, a house is in ruins and streets are strewn with debris after lethal storms swept across NSW.

The wild weather hit the Sydney and Illawarra coastline on Saturday afternoon before it claimed a 15-year-old boy's life in the Hunter region.

The teenager was walking out of the ocean at One Mile Beach, near Port Stephens, when he was struck by lightning about 5pm (AEDT).

Family members worked to try and save the boy until emergency services arrived but he died on the beach.

An hour earlier a 50-year-old man was struck by lightning standing outside a house at Birrong in Sydney's south-west.

He was taken to hospital in a serious condition.

A lightning strike also sparked a house fire in the south-west suburbs.

A woman felt a tingling sensation after her two-level Lansvale home was struck but managed to escape the house before it was ravaged by fire.

The storms also came with damaging winds that brought down power lines, trees and ripped off roofs.

The State Emergency Service (SES) logged more than 1100 jobs by Saturday night with the Penrith, Blacktown and Liverpool areas the hardest hit.

Wind gusts reached up to 100km/h in Sydney and ripped part of a roof off a medical centre in Kingswood.

More than 25,000 homes in Sydney were also left without power, according to Endeavour Energy.

SES spokeswoman Sue Pritchard said on Saturday night volunteers had gone to more than 200 calls and had another 900 to go.

"People that have been away for the day and come home may find damage so we could see an influx of calls (on Sunday)," she told AAP.