There has been hail across Sydney this afternoon, from Newtown to Mt Druitt, with State Emergency Services responding to 145 calls for assistance since 4pm.
The Bureau of Meteorology has issued a severe thunderstorm warning for most of south eastern NSW, including Sydney and the ACT.
The hail is expected to subside this evening, according to SES spokeswoman Tanya Arginovsky.
The heaviest hit area so far has been Mt Druitt, which accounted for 82 of the state's 145 emergency calls. Approximately 11 calls came out of Blacktown, according to Ms Arginovsky.
SES have advised that people secure loose items that could be blown away by strong winds and move cars away from trees and powerlines.
Blackheath experienced about one to two centimetres of hail this afternoon and is on the threshold of "severe hail", defined by the Bureau as two or more centimetres.
Most of Sydney is expected to experience heavy rainfall this evening.
Although the storm is supposed to move offshore by the end of the day, there is a risk of continued hail and potential flash flooding, according to Bureau of Meteorology forecaster Zach Berry-Porter.
"We're getting towards the end of the thunderstorm season, and it is a bit strange to see weather like this," said Mr Berry-Porter.
The weather is unlikely to reach the severity of the three-day storm earlier this week that led to a natural disaster being declared in 12 parts of the state.
"It's looking like things are going to stabilise on Sunday," he said.
"It will be a cooler day with a chance of showers across Sydney."
