Emergency clean-up crews have fielded scores of calls for help as thunderstorms continue to menace eastern NSW.

Wild storms were detected above northern Sydney on Friday evening, and the Bureau of Meteorology warned that suburbs along the NSW Central Coast and northern beaches were likely to be lashed with heavy rains and damaging winds.

By 7pm, a severe thunderstorm warning remained for stretches of eastern NSW including the Hunter, metropolitan, Illawarra and Northern Tablelands districts.

The State Emergency Service (SES) received 107 calls for help in the four hours from 2pm (AEDT) – nearly half came from suburbs in southern Sydney – and expected to hear from more homeowners as they returned from work.

Todd Burns of the SES told AAP the rough weather was expected to continue throughout the weekend.

But conditions could change quickly.

“These storm cells can pop up out of nowhere and can be quite hard to predict,” he said.

Strong winds uprooted a large tree on busy inner-city Devonshire Street about 1.30pm, bringing down powerlines and hitting a man.

Paramedic Lauren Capanna told the Seven Network a pedestrian in the path of the falling tree escaped with minor injuries.

Meanwhile, lightning struck railway signals between Lidcombe and Strathfield, causing train delays.

Heavy rain caused dangerous flash flooding in southwestern Sydney.

“In Camden we’ve had 30 millimetres in 30 minutes, which is a pretty heavy downpour,” Mr Burns said.

The SES warns people against driving or walking into floodwaters.

Fair Trading Commissioner Rod Stowe warns residents whose properties are hit in the storms to beware of unlicensed tradespeople who might offer repair services.