Sydney's north and northern beaches bore the brunt of wild weather on Sunday afternoon. Residents reported tornado-like scenes and widespread blackouts.
About 20,000 homes and businesses from Palm Beach to Freshwater lost electricity at about 1pm, and Ausgrid crews spent all afternoon working to restore the power.
''There is quite a bit of damage to the network, we've seen whole trees coming down, a lot of falling branches taking out wires and some lightning strikes,'' an Ausgrid spokesman said.
''We have crews working at multiple locations and power will be restored gradually. It will be well into the late afternoon and early evening until we have power back in all areas.''
The storm lasted for under an hour in most areas but brought flash flooding, winds of up to 100km/h and falling trees. Power lines and trees fell on Pittwater Road in Mona Vale and around Duffys Forest and Terrey Hills.
Traffic lights were blacked out in several spots, according to the Live Traffic NSW website.
As the storm moved north to the central coast, Ausgrid also reported 1900 homes at Wyoming and Lisarow had lost power.
Ben McBurney, a meteorologist at Weatherzone, said the northern suburbs were hit the hardest, with wind gusts reaching 89km/h at Terrey Hills and rainfall totals of about 10 millimetres.
But the storms were moving so fast that while the rain was heavy, it did not last long.
''They're really flying,'' Mr McBurney said as the storm front passed.
Wind speeds of as much as 137km/h were earlier recorded at Thredbo in the state's south-east.
State Emergency Service volunteers were expecting to be called to 300 jobs by the end of the day, mainly around the northern beaches, said spokesman Todd Burns.
One of the biggest jobs was removing a tree that fell on a car on Mona Vale Road. ''This storm has hit Sydney so quickly, all our volunteers have just had to scramble together to get each job covered as quickly as possible,'' he said.