NEW YORK, US - FOUR giant artificial waterfalls cascaded into the water off Manhattan on Thursday in a public art project the mayor said could generate US$55 million (S$75 million) in economic activity for New York City.

'New York City's historic harbour has been turned into the most unexpected and intriguing waterfall destination between Niagara Falls and Victoria Falls,' Mayor Michael Bloomberg said at a news conference marking the opening of the falls.

He admitted that when the project was first pitched to him, his first thought was: 'What on earth are you talking about?'

Three of the waterfalls cascade into the East River and New York Harbour from free-standing scaffolding towers. The fourth is below the landmark Brooklyn Bridge. The project by Danish artist Olafur Eliasson will be in place until Oct 13.

The falls range in height from 30 to 40 metres - around the same as the Statue of Liberty from head to toe, and from 9 to 24 metres wide.

Tour companies are offering special trips to view them, ranging from a US$10 boat journey lasting 30 minutes with official sponsor Circle Line Downtown to a US$50,000 'Waterfalls Package' from rival Circle Line Sightseeing Cruises.

The latter includes a private boat trip, champagne, diamonds, dinner for two and a night in a luxurious hotel.

The falls are also visible from various vantage points on land, including bridges and highways, and the city is handing out bicycle maps.

Visitors can call a toll-free number, 311, to hear Eliasson talk about the falls as they view them.

Eliasson said he was happy and relieved that the project, two years in the making, was finally ready.

'It's been quite a journey,' he said at the news conference. 'Even though it's a scaffold standing on shoreline, sucking water up to the top and letting it fall right back down, it's been a big challenge to achieve this.'

Mr Bloomberg said the US$15.5 million project, funded by private donations and a US$2 million grant from the Lower Manhattan Development Corporation, would help business, from restaurants to hot-dog stands, at a time when the economy needs a boost.

'We estimate the project will generate more than US$55 million in economic activity for our city,' he said.

City officials are hoping to emulate the success of Christo and Jeanne-Claude's project, The Gates, which drew around 1.5 million visitors to the city in February 2005 to view some 7,500 saffron panels draped through Central Park.

Eliasson, who was born in Copenhagen in 1967, is best known for his 2003 installation The Weather Project at the Tate Modern in London, which was a giant sun made of mirrors, lamps and mist.

Perhaps mindful of a day earlier this month when two men climbed a 52-story skyscraper in Manhattan, Mr Bloomberg urged visitors to exercise common sense: 'Under no circumstances should anyone try to climb the falls or swim around them.' -- REUTERS