Severe thunderstorms, hail set to hit NSW

Less than 24 hours after one wild weather battering, NSW residents are being told to batten down again.

Another severe thunderstorm was on its way and due to sweep the majority of the state within hours, forecasters said on Thursday afternoon.

The Bureau of Meteorology predicted large hailstones, damaging winds and heavy rainfall that may cause flash-flooding.

Sydneysiders were still mopping up from Wednesday's big wet that caused flight and traffic delays and left up to six people affected by lightning strikes.

BOM forecaster Neale Fraser predicted the storm would be stronger than the previous day's.

"Once (the hail) gets as big as a $2 coin in diameter, that's causing problems," he said.

Mr Fraser said the storm would spread across most of inland NSW within hours, and was likely to extend to coastal regions by late afternoon.

The State Emergency Service was advising people to steer clear of creeks and storm drains, move cars under cover or away from trees, stay indoors away from windows, and unplug computers and appliances.

The weather is set to continue on Friday and into the weekend.