New York, Jan 1 - Hundreds of thousands of New Year's Eve revellers braved freezing temperatures and snow mixed with rain to sway to John Lennon's "Imagine" before counting down the New Year as the traditional crystal ball dropped above Times Square.

The celebrants, whose numbers were estimated as high as one million, also braved tight security to enter the New York tourist hotspot to watch the nearly four-metre-wide illuminated ball swirl with the changing colours of blue, pink and yellow as it descended from the top of a pole on the Times Square No. 1 building beginning 60 seconds before midnight.

As the clock struck 12, fireworks shot from the top of the building as couples kissed in the packed square below in the first seconds of Friday morning and confetti showered on the crowd, which then began singing and dancing to Frank Sinatra's "New York, New York" and Ray Charles' rendition of "America".

Hundreds of New York City police and armed troops were deployed to provide security in and around Times Square. Barricades went up early Thursday, blocking traffic from the plaza, which is also the focus of millions of television viewers from around the United States who tune in to count down the New Year.

Security was tight. In addition to armed troops deployed in the vast subway network serving the city's 8.5 million residents, others were sent to the city's two main airports, La Guardia and JFK International Airport.

With the recent bombing attempt on a US airliner on Christmas Day, nerves were especially on edge and the airspace over Manhattan was tightly patrolled by police helicopters.

Police who locked down Times Square were also equipped with radiation and biological detectors.

Revellers bundled with heavy winter coats were not allowed to carry backpacks or large bags into barricaded areas. Those who left before the dropping of the ball were prevented from returning to their original sites, and alcoholic beverages were banned.

City Hall officials, led by Mayor Michael Bloomberg, who was sworn in Thursday to a third, four-year term, were joined by selected students from 12 public schools ranked among the 100 best in the United States, news reports said.

This year's ball's 2,600 Waterford crystals were lit up with LED lights with the crystals designed with interlocking ribbon patterns woven into a Celtic knot called Let There Be Courage. The knot in different colours has been also used in anti-AIDS campaigns and to welcome home troops from deployments abroad.

The mass of revellers was expected to leave behind more than 40 tons of debris, including party hats, noisemakers, confetti and streamers.

The city planned to send in 150 street sweepers immediately after midnight, armed with mechanical sweepers, trucks and leaf blowers to clean up Times Square for New Year's Day.

"We generally have the place cleaned up early in the morning," Bernard Sullivan, an official of the Sanitation Department, said on a local news broadcast.

"There might be some tidying up on the side streets that continues through the morning, and we have people in place to go right through tomorrow to make sure everything is in tip-top shape," he said Thursday.

But the bad weather in New York dampened prospects of a "blue moon" over Times Square on New Year's Eve.

Weather forecasters and astronomers said this week that a blue moon was to add to the New Year's Eve celebrations in most of the world.

The blue moon phenomenon occurs when there are two full moons within a month, which happens every two and a half years. The last full moon was Dec 2, but a blue moon, which has nothing to do with colour, is rare on New Year's Eve. (dpa)