Winds exceeding 100 km per hour and heavy rain hit Sydney and much of NSW Sunday night, and widespread blackouts affected people across the state, reports Xinhua news agency.
The Bureau of Meteorology (BoM) forecast more severe thunderstorms for northeast NSW on Monday.
The NSW State Emergency Service (SES) said on Monday that it was called out to 278 incidents across the state, 81 of which were in Sydney.
In Carinda, a small town of 93 people almost 500 km northwest of Sydney, three commercial properties were destroyed, with their roofs ripped off by winds exceeding 150 km per hour.
A concrete and steel road plate measuring one square meter was dislodged from the Sydney Harbour Bridge during the storm shortly after 8 p.m. local time on Sunday, damaging 25 cars and causing traffic delays on the bridge.
Secretary of Transport for NSW Josh Murray said the state government would pay to repair the vehicles.
"It was a nightmare," Murray told Nine Radio on Monday. "Let me apologise to anyone whose car was damaged or anyone else who was caught up for about two hours."
Over 20 flights into Sydney on Sunday were cancelled, and others from Qatar and Fiji were diverted to Brisbane.