Bill Expected To Top $20 Million After "Catastrophic" Hail Storm

The bill for the "catastrophic" hail storm that struck Sydney and other parts of NSW is expected to be more than $20 million with 15,000 people lodging claims so far.

Multiple storm fronts converged on the Hunter Valley, Wollongong and Sydney on Thursday afternoon, prompting a severe weather warning from the Bureau of Meteorology.

Tennis ball-sized hailstones smashed into homes and cars in Sydney's west around 5pm while golf ball-sized stones battered the city's inner suburbs less than an hour later.

The Insurance Council of Australia declared the incident a catastrophe at 7.30pm, triggering support for affected residents.

Tens of thousands of homes were left without power and the full scope of the damage is not yet known.

The ICA said on Friday some 15,000 claims worth about $18 million had been lodged as at 6.30pm Thursday and more were expected on Friday.

The council said there had been "extensive damage" to cars and homes from Sydney's west to Bondi Beach.

Windshields were smashed, roofs damaged and both cars and homes impacted by flash flooding.

The primary thunderstorm which affected the Sydney basin began to ease about 7.45pm.

Endeavour Energy reported 20,000 homes and businesses in its network were without power from the Blue Mountains, through Sydney's west and up to the Hawkesbury.

Around 200 electrical hazards were left in the wake of the storm after power lines came down.