Sydney residents are assessing the damage on Friday after multiple severe thunderstorms pummelled the city on Thursday evening, raining down cricket ball-sized hailstones that dented cars and smashed through windows across the city.

Emergency service workers said it was the worst hail storm to hit the city in 20 years, as the Insurance Council of Australia declared the event a “catastrophe” and said a large number of claims had already been lodged.

The ICA said on Friday that about 15,000 claims had been lodged, and the repair bill was expected to exceed $80 million. Most of the damage related to motor vehicle damage, the ICA said.

“It is simply the ferocity of the hailstorm and it is pretty clear … that the damage is likely to be widespread and catastrophic in its proportions,” Campbell Fuller, a spokesman for ICA, said.

About 2000 homes and businesses on the Central Coast remained without power on Friday morning, while another 5500 were without power in the Hawkesbury and Lithgow regions as Ausgrid and Endeavor Energy crews worked to restore services to the respective areas.

Cars had their windows punched in by the giant hailstones as people across the city took cover at the height of the wild weather. At Bondi, surfers jumped off their boards in the water and used them to protect themselves as the ice splashed into the water around them.

Canberra resident Eliza Berlage was driving to Sydney for Christmas and New Year when she was caught in two consecutive hailstorms that left the back windscreen of her car “smashed”.

The first hailstorm left her with a chip. When the second, bigger one hit, she had just turned off the freeway at Liverpool and looked up the nearest service station to take shelter.

As “golf ball-sized” hail rained down on her, she arrived at the servo only to find more than a dozen other cars had the same idea.

“I only got halfway under, so that’s why my back windscreen was smashed,” she said. Christmas gifts and luggage were wet.

Unable to get a tow-truck, she taped up the back windscreen with plastic bags and called her insurer, only to be told the windscreen wouldn’t be replaced until after Christmas, possibly into the New Year.

As social media lit up with pictures of enormous hailstones, white-covered backyards and smashed cars, the SES received more than 500 calls for help from residents in Sydney’s eastern, inner and western suburbs.

Hailstorms are typically among the most costly weather events for insurers – and among the hardest to forecast.

The storm drew immediate comparisons with the costliest event in Australian insurance history from April 1999 that struck from Bundeena to Darling Point with hailstones of more than 9 centimetres, leaving a damage bill of more than $1.5 billion.

Wayne Wilson from Rose Bay had no time to move his car under cover when “baseball-sized” hail started pummelling his street.

“There was no time to get out and move the car unless you wanted to get hit by hail,” he said.

“Better to have the dented car than get knocked out.

He said the massive hailstones only fell for about 45 seconds amid the five-minute long hailstorm.

“I’ve been out there and had a look. My car’s covered in leaves but there is definitely going to be some hail damage on the car,” he said.

His neighbours have tears in a marquee set up in their backyard, he said.

“Hopefully insurance will cover it if there is damage.”

Paddington resident Christopher Sharp said the hail “went from the size of golf balls to cricket balls” and smashed a skylight in his home.

“It suddenly felt quite foolish to be gawping at the windows,” he said.

‘Not your normal thunderstorm’

The biggest hailstones recorded by the weather bureau were about 8cm in size, around Berowra in Sydney’s north. But there were multiple reports of stones around 5cm, including at the Bureau of Meteorology offices in Surry Hills, said forecaster Jake Phillips.

It “definitely was not your normal thunderstorm day”, he said.

“It came through in several waves over several hours. Often what you tend to get is one or two really large storms that move through,” he said. “The first lot of storms came through Sydney about 4pm and some suburbs missed out and some got hit – but then there was continuous storm activity for an hour or two after that, and quite a lot of those storms were severe in nature.”

Public transport ground to a halt during the evening commute, with light rail services abruptly suspended just before 6.30pm, sending passengers on board a Central to Dulwich Hill service out into the wet at Convention.

The wild weather also caused the partial closure of the T3 line between Bankstown and Sydenham due to urgent power supply repairs, with bus companies used as replacement services. Services travelling away from the city on the Illawarra line were also affected due to urgent track repairs at Hurstville.

Some train drivers were just forced to stop in their tracks due to poor visibility.

Mathew Hewson was on board a train from Parramatta to Homebush that was forced to stop for 20 minutes just after 6.30pm because the driver couldn’t see.

“It just got really dark and the train stopped all of a sudden,” he said. “It really came down and hailstones and everything.”

About 60 flights at Sydney Airport were cancelled during the height of the strom, while thousands of homes were blacked out. At 7pm on Thursday, Ausgrid reported more than 7000 customers were without power across Sydney and the Central Coast.

Assistant Commissioner Scott Hanckel from the NSW State Emergency Service said the organisation received about 1800 calls for help during the storm. The hardest hit areas appeared to be Berowra Heights, Hornsby and Liverpool.

“This was some of the worst I have seen in my 20 years,” he said.

The heavy downpour brought flooding to major roads in the city’s north and west, including the M4 at Auburn, Ryde Road at West Pymble and Macquarie Street, Windsor.

Sydney residents should get some reprieve on Friday, with showers – but no more thunderstorms – on the forecast.