NEW YORK (Reuters) - More than a million people in New York's Times Square hailed the arrival of 2016 early on Friday (Jan 1) with kisses, cheers and a measure of relief as America's biggest New Year's Eve celebration unfolded without a hitch under a blanket of unprecedented security.

The transition to the new year was marked by the descent of the traditional lighted crystal ball from atop a skyscraper at the centre of the famed Manhattan crossroads, the climax of an annual rite of winter dating back to 1904.

With memories of the deadly attacks in Paris and California still fresh, police took extraordinary measures to ensure security at a gathering that has come to define the New York experience for many visitors to the largest United States city.

But the event, broadcast live on national television, went off without a hint of trouble, as a festive mood prevailed despite - or perhaps because of - the heavy police presence.

Hours before official festivities began at 6pm local time, people from all over the world began to assemble in the square.

"This is the centre of the world on New Year's Eve," said Mr Rick Milley, 60, who traveled from Boston with his wife, Debbie, 59, to ring in the new year in Times Square.

"This was on our bucket list," Mrs Milley said as the couple took pictures of themselves using a selfie stick.

The pair have spent the holiday in New York before but never in Times Square, a year-round tourist draw, filled with chain stores, family restaurants and flashy advertising displays.

About 6,000 uniformed and undercover police officers, 500 more than last year, were expected to flood the area, with the force bolstered by mounted patrols, bomb-sniffing dogs, radiation detectors and hundreds of surveillance cameras.

The city for the first time was deploying its new Critical Response Command, which includes more heavily armed officers.

The unit is trained to detect and respond to attacks, such those in Paris that killed 130 people on Nov 13, or the rampage in San Bernardino, California, in which 14 were slain.

The US Department of Homeland Security has ranked the Times Square celebration as a level-2 concern on its five-point scale of security risks for major public events, a designation one step below the top-rated level-1 classification given Friday's Tournament of Roses Parade in Pasadena, California.

About 700,000 people are expected to turn out for the 127th Rose Parade.

Department officials have said they are unaware of any specific, credible threat to the Times Square gathering.

The famous New Year's Eve ball, which is 3.6m in diameter and weighs nearly 6 tonnes, descended on a pole mounted on top of One Times Square, a narrow wedge of a building along 42nd Street at the southern end of the square.

Mayor Bill de Blasio pushed the button that began the descent, leading to the 60-second countdown to midnight, when a giant illuminated "2016" sign flashed on, signaling the beginning of the new year.

By early evening, crowds organised into neat pens formed by police barricades stretched for many blocks up Seventh Avenue and Broadway north of One Times Square.

From a vantage point about 20 floors above, the revelers appeared to be tucked neatly into block-long honeycombs encircled by uniformed officers and support workers dressed in bright red coveralls.

Cheers reverberated through the area as images from the entertainment stages flashed on a giant screen mounted on the building just below the pole supporting the crystal ball.

On occasion, fireworks exploded above, sending flashes of light and wafts of smoke through the square.

"I always wanted to come here, but never took the chance,"said Mr James Gomez, 39, of New Haven, Connecticut, as he surveyed the area with friends looking for a prime viewing spot.

Mr Gomez came to Times Square even though he said he was concerned about the area being targeted in an attack. "I'm scared," he said.

In the hours before midnight, musical artists such as Carrie Underwood and Jessie J performed on stages set up in the area.

More than 100 million Americans and 1 billion people worldwide were expected to watch the festivities on television.

In Rochester, New York, a 25-year-old man accused of planning to attack a restaurant on New Year's Eve was arrested on Wednesday and charged with attempting to provide support to Islamic State in Iraq and Syria (ISIS), the US Justice Department said.

Afterwards, Rochester, about 530km north-west of New York City, cancelled its New Year's Eve fireworks display.

Before entering Times Square, visitors were required to pass through tight security checkpoints, with police stopping anyone from carrying backpacks and large bags while searching smaller bags and scanning people with metal detectors.

The tradition of gathering in Times Square to celebrate the new year began in 1904, according to the Times Square Alliance, the area's business-development association.

That was the year that the New York Times opened a new headquarters building at One Times Square and the city officially renamed the square after the newspaper.