Sydney NYE Revelers Hit With Pre-Show Downpour

Thunderstorms have drenched crowds and lit up the sky above Sydney Harbour as the city counts down for its spectacular New Year's Eve fireworks display.

The storms rolled in just before sunset, bringing 8mm of rain and dozens of lightning strikes and forcing the cancellation of the 8pm aerial flyover display.

The night's two firework shows are still scheduled for 9pm and midnight, with crowds of more than one million people expected to watch across the city.

Tens of thousands of people are already crammed into vantage points around the harbour, including at the Sydney Opera House, Mrs Macquaries Point and Kirribilli.

NSW Police have assured revellers that while the terror alert remains at probable, there is no specific threat.

"We put obstacles between those large crowds and vehicles to ensure people can get in and out safely and enjoy their night in safety," Acting Deputy Commissioner Mark Walton told reporters in Sydney on Monday.

Dedicated revellers arrived early on Monday to set up picnic blankets at popular spots including the ends of the bridge, the Opera House and Mrs Macquarie's Chair.

Jeroen van Druten and his wife Miranda - holidaying in Australia from the Netherlands - have watched Sydney's fireworks on television for years.

By 11am they had parked themselves under the bridge at the Rocks with a bag of supplies as temperatures climbed toward 30C.

"You hear from everyone it's very busy, crowded, so to get a good spot you have to be early," Mr van Druten told AAP.

"It was on our bucket list."

Sydney Lord Mayor Clover Moore took aim at the state government for charging to view the famous fireworks display at some harbourside locations. "All the city-owned sites are free and any of those that are ticketed are ticketed by Property NSW or the Royal Botanic Gardens," she told reporters on Monday. "I frankly think it's outrageous they are trying to make money out of something we are putting on to bring the community together harmoniously."

Almost 20 government-owned sites are ticketed with the Botanic Gardens, for example, charging $335 for its Harbour Hoopla event.

Property NSW hit back saying only one of the venues it manages - Hickson Road Reserve - requires paid entry and the ticket price pays for live music and security.

Comment was also sought from the Botanic Gardens.

This year's $5.78 million Sydney NYE show will comprise 8.5 tonnes of fireworks, more than 100,000 individual pyrotechnic effects and 35,000 shooting comets.

The theme is the Pulse of Sydney with the display featuring gold, silver and purple pyrotechnics.

The soundtrack will feature hits from Australian and international artists reaching a crescendo after midnight with (You Make Me Feel Like) A Natural Woman made famous by Aretha Franklin who died in August.

Australia's iconic landscapes will also be celebrated with an animation inspired by the rock anthem Great Southern Land beamed onto the harbour bridge's pylons at 11pm before the main 12-minute firework display lights up the city's skies at midnight.

The visual displays will run all night spanning the entire bridge for the first time with more than one billion people globally expected to watch on television.