Wild storms have wreaked havoc across Sydney and much of eastern NSW, dumping heavy rain and ripping off at least one roof.

There were also reports of flash flooding, trees down across the city and rapid temperature drops as the storms hit on Monday morning.

NSW SES said it had already been called to 270 jobs by 2pm as the storms cut across the city. They were expected to move north further into the afternoon.

“NSW SES units have been busy responding to jobs relating to roofs coming off properties and trees falling down. One of these in particular was at Mortdale, where a large part of a workshop roof was removed due to the damaging winds. Thankfully no one was injured,” NSW SES Assistant Commissioner Sean Kearns said.

“These winds bring great risk to already saturated soils, creating a perfect storm for trees to get pulled out and damage property or roads.”

“People in the impact locations should move cars undercover and away from trees and powerlines and secure loose items around your home.”

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Forecaster Weatherzone said Sydney started Monday with its warmest morning of summer so far. The city reached 29.6 degrees just before 10am, while it was above 30 in other areas from Sydney Airport to Penrith.

Shortly after a line of thunderstorms moved across the Sydney metropolitan area, bringing strong squalls, hail and heavy rain. Temperatures dropped rapidly as the first storms moved in.

“A whopping 21.6 millimetres of rain was recorded in just 14 minutes between 10.46am and 11am at Observatory Hill, while 95km/h wind gusts were reported as storms ripped through,” Weatherzone said.

“Temps dropped to the low-20s or high-teens in most parts of the Sydney region after the first wave of storms passed.”

The Bureau of Meteorology has issued warnings of severe thunderstorms for much of NSW. It forecast 90km/h winds across parts of the state, including in Bowral, Braidwood, Bathurst, Katoomba, Goulburn and Cooma.

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The bureau is also expecting peak gusts of 125km/h in NSW’s higher alpine areas. The winds are expected to extend across the border into north-eastern Victoria.

It came after an earlier warning of days of dangerous weather for the state, including Sydney.

With the storms have come cold conditions. Graziers across the south-west slopes, Snowy Mountains and ACT are being warned this week’s weather could be deadly for lambs.

Rain and thunderstorms are forecast to hit Sydney on Monday morning and last into Tuesday or even Wednesday.

Mr Kearns said flash flooding remained a concern as thunderstorms could bring bands of rainfall to catchments across the state, in particular, north-eastern NSW.

“Now is not the time to be complacent with flood warnings,” he said.

“We have seen fast moving flash flooding enter towns across NSW in the last few months from storms and rainfall.”

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The SES said flood operations continued in western and southern NSW, with towns still cut off by waters.

There were 41 flood warnings in place across NSW on Monday afternoon, including two emergency warnings.

The NSW SES said last week it had clocked more than 20,000 requests for assistance since record flooding began across inland NSW three months ago.

Hardest hit areas include central-western NSW, along the Lachlan River where there have been more than 3000 requests for help (Forbes and Condobolin) and northern NSW, along the Namoi (Wee Waa) and Mehi (Moree), here there have been more than 1600.

-with AAP