Sydney's CBD was plunged into "apocalyptic" darkness mid-afternoon and lightning strikes lit up U2's concert in the city on a day of remarkable weather conditions in the NSW capital.
The city was eerily dark by 5pm on Friday ahead of the thunderstorms as storm clouds mixed with the lingering smoke from NSW bushfires that had settled across the city, including from one blaze at nearby Gospers Mountain.
Thousands of homes on Sydney's lower north shore lost power as thunderstorms affected the region's electricity grid on Friday.
The Bureau of Meteorology says the thunderstorms began brewing in the Blue Mountains on Friday afternoon, as moisture from the north met with triggers such as converging winds.
The storms then travelled west towards Sydney, a bureau spokeswoman told AAP.
Sydneysiders took to social media to share their surprise at the changing weather.
Amanda posted on Twitter that Sydney was dark "almost like an apocalypse".
@ErkenciKusGifs said on Friday evening that Sydney was "crazy".
"It's pitch black hours before sunset, there's heavy smoke in the air, lightning and thunder, and sirens going past every few minutes. Very eerie. Mother Nature isn't happy," they posted on Twitter.
"Whoever turned out the lights in Sydney, please turn them back on - some of us are trying to read," @hannahplusone wrote.
Conditions have eased in Sydney but remained late on Friday night in some parts of the state, including Newcastle and near the Queensland border.
About 20,000 homes in Sydney suburbs Mosman and Castle Cove lost power on Friday afternoon, an Ausgrid spokeswoman told AAP.
Lightning strikes also lit up rock band U2's concert at the Sydney Cricket Ground.
"(hash)U2 is giving (hash)Sydney a free concert tonight with thunder and lightning as backup. It's epic," (at)boswellryan posted on Twitter.
Fans attending the concert were shown an emergency warning on screens at the SCG.
"Bad weather is approaching, please remain calm," the signs read.
The NSW Rural Fire Service posted on Twitter in the evening that storms were bringing lightning, creating new fires.
Weather conditions also affected flights at Sydney Airport with diversions, delays and several flight cancellations.
Australian Associated Press