Sydney has been spared the brunt of the severe thunderstorms this afternoon, with the wild weather hitting the state further north.

A thunderstorm warning was still in place for NSW, according to the Bureau of Meteorology, with storms affecting areas around Narrabri right down to Newcastle.

Sydney still had a roughly 30 per cent chance of thunderstorms later this evening, but the chance of a severe storm was "much lower", a spokesperson for BOM said.

Further north, hail two centimetres in diameter hit Bar Beach in Newcastle around 4.30pm this afternoon, and 42.5mm of rain was recorded about 15km inland at Macquarie College, according to BOM.

Wind gusts of 82km an hour had also been recorded in Coonamble and Narrabri.

By 3pm the State Emergency Service had received about 20 calls for help, mostly due to fallen trees and branches and leaking roofs.

"We are expecting quite a high volume of calls this afternoon and this evening," SES spokesman Neil Wilbin said.

While the brewing storm made for a nice photo opportunity, the SES says people in affected areas should stay indoors and away from windows.

Residents in affected areas are also advised to move cars under cover or away from trees and to secure any loose items around the house. The SES also advised motorists to take caution on wet roads.

"There's a lot of motorists on the road, travelling home after the long weekend, so we'd encourage them to take care, slow down and avoid travelling if they can," Mr Wilbin said.

During a thunderstorm it is also advised to keep clear of fallen power lines, unplug electrical appliances and avoid using the phone, the SES says.

For emergency help in floods and storms, ring the SES on 132 500 or if the situation is life-threatening call 000.