Much of Australia's New South Wales has been lit up by huge thunder and lightning storms, which killed at least one person.

Sydney was plunged into near darkness as the fast moving storms blew in at about 6pm (8pm NZT) on Saturday. The nature of the first storm system was unpredictable, and saw heavy hail, lightning, thunderstorms, and rainfall of between 5 and 30 millimetres spattered across much of the region.

Dramatic photos showed the Sydney Harbour Bridge being hit by bolts of lightning though the storms only lasted about an hour before they moved north-east, up through the Hunter region and headed out to sea.

CAMERON SPENCER/GETTY IMAGES A large storm front makes it's way towards the city ahead of the Invictus Games in Sydney.

"There are very widespread storms across most of the state as this low pressure system moves through," Bureau of Meteorology forecaster Jake Phillips said.

READ MORE: Severe storm fails to dampen Invictus Games opening

"We just need to watch individual storm cells as they evolve ... it's difficult to say with rainfall because it's quite variable from place to place. [Between 5 - 30mm] is a wide range I know, but that is just the nature of thunderstorms."

MARK EVANS/GETTY IMAGES The nature of the first storm system was unpredictable, and saw heavy hail, lightning, thunderstorms, and rainfall of between 5 and 30 millimetres spattered across many regions.

The state's far west suffered the brunt of the thunder and lightning earlier on Saturday afternoon.

A 53-year-old man died in Geurie, about 30 kilometres from Dubbo, just after 2pm after being struck by lightning at a recreational ground.

'MORE TYPICAL OF SUMMER'

MARK KOLBE/GETTY IMAGES Torrential rain from leads to the cancellation of the remaining of the days events during the X Games in Sydney.

Sydney was in the midst of its most humid October in at least 15 years, according to Brett Dutschke, senior meteorologist at Weatherzone.

"It's been more typical of summer [and] definitely unusual for October," he said.

Afternoon humidity levels had been averaging about 70 per cent compared with the October average of 55 per cent, Dutschke said, citing readings from Sydney Airport.

Saturday provided Sydneysiders with the unpleasant end of the humidity scale. Temperatures nudged 30 degrees Celsius in parts of the city but felt a couple of degrees warmer because of the greater difficulty of shedding heat - at least before the storms rolled in.