Sydney's skies opened as the tall ships sailed into Sydney Harbour to launch a once-in-a-century "mega-weekend" that's tipped to rival the 2000 Olympics.
Eighteen visiting warships, 17 tall ships and 19 Royal Australian Navy vessels are taking part in the historic International Fleet Review, which runs until October 11.
The maritime spectacular on Saturday will also feature more than 60 aircraft, 10 military bands, 8000 sailors, a huge fireworks display and a red-headed prince.
NSW Premier Barry O'Farrell said the International Fleet Review would showcase the city and its magnificent waterways to 1.4 million visitors - including Prince Harry, who is set to drop by during his whirlwind royal tour of Australia.
"The fireworks and the light show will be bigger than what we see on New Year's Eve and that's one of the great attractions that people can expect," Mr O'Farrell told reporters on Thursday.
"People are excited. It's a great weekend to be in Sydney. It's going to inject $50 million into this city and the state's economy."
NSW Tourism Minister George Souris said the event would be one of the biggest ever hosted in Sydney.
"This weekend is perhaps the mega-weekend of them all," he told reporters.
"The city and the state is in big welcome mode at the moment and we look forward to greeting all of the visitors who are going to come from all parts of Australia and the world for this incredible weekend of events ... This will rival the Olympic effort."
As rain bucketed down at one of the city's best vantage points, Mrs Macquarie's Chair, International Fleet Review director Nick Bramwell said the sailors would take the bad weather in their stride.
"This is only fresh water, so this is fine," he joked.
"The sailors are going to have fun ... there's approximately 8000 of them from all over the world, we've got sailors from 17 countries plus Australian sailors from different parts of the country, so we're sure that they will be on their best behaviour."
NSW Police Superintendent Craig Sheridan said extra police were on hand to ensure spectators behaved, too.
"We have additional police right across the operational footprint rostered for duty over the course of the long weekend and right through to next Friday, for the finish of the event," he said.
"We're expecting large crowds in a family-friendly atmosphere."
Undeterred by the rain, backpackers, tourists and locals mingled by the harbour on Thursday morning as they waited for the tall ships to come in.
Janet Rigby brought her granddaughter along to watch from the foreshore.
"I was interested in the history of the day and I thought it would be a lovely experience for us both to watch the tall ships come through," she told AAP.
But the pair were forced to take shelter when the deluge hit.
"I was excited but I'm not too happy about the weather," young Alexis Rigby conceded.
The review commemorates the arrival of the Royal Australian Navy fleet in Sydney for the first time 100 years ago, in October 1913.