Huge crowds braved biting cold in New York to watch the traditional drop of the crystal ball on Times Square, kiss, and cheer in 2009.
Security was heavy as an estimated million people poured into central Manhattan for the street party, despite icy temperatures and deepening economic woes across the United States.
Former US president Bill Clinton and his wife Hillary Clinton, tapped by incoming president Barack Obama as secretary of state, joined New York Mayor Michael Bloomberg to release the famous Times Square ball.
Crowds shouted out the last seconds of the year as the huge orb, glowing and glittering through 2,668 crystals and more than 32,000 red, blue, green and white LED bulbs, descended a special pillar.
Couples embraced, then joined the Clintons in dancing to "New York, New York" and other classic songs. Two tons of confetti poured into the streets from skyscrapers and fireworks thundered into the starry night.
Tim Tompkins, president of the Times Square Alliance, estimated the crowd, stretching as far as Central Park about a mile (1.6 kilometers) north, at between 750,000 and a million.
Earlier, the Jonas Brothers pop trio sang to revellers, many of them wearing blue floppy top hats and outsized sunglasses, while local TV networks homed in on couples practicing their midnight kisses.
Despite the festive atmosphere, this was a chilly start to the new year, with temperatures of about 18 degrees Fahrenheit (minus eight Celsius), even lower with the wind chill.
Security was exceptionally tight amid worries about what experts say is the potentially vulnerable White House transition period.
New York police commissioner Raymond Kelly said that in addition to standard patrols there would be watchtowers and teams with radiation and biological detection equipment.
Backpacks and alcohol were banned in the area.
"You'll see a lot of uniformed officers. As I said, you'll see a lot of our equipment on display," Kelly told CNN television.
"What you won't see is officers in plain clothes. We have what we call a counterterrorism overlay. We'll have a lot of observation posts that will be manned. We have our helicopters in the air."
The city police chief said the November bloodbath in Mumbai, where 172 people were killed by a handful of well-trained gunmen during a three-day rampage, was an important lesson.
"We sent people to Mumbai. We got very specific information as to what happened there. We'll make some adjustments that may not, the public may not see.... We've learned from Mumbai," Kelly said.
An additional layer of security was provided by the Secret Service which gives round-the-clock protection to the Clintons.
Hillary Clinton is a New York senator and, if confirmed, is to take up her new job as top US diplomat after Obama's January 20 inauguration.