Security checkpoints at the city's bridges and tunnels were beefed up in anticipation of the celebration, and the New York Police Department planned to deploy 1,500 rookie officers to blend into the crowd at Times Square.
Cities prepared for celebrations both traditional and unusual. Atlanta was expecting to welcome thousands to its downtown, where a giant peach is dropped every New Year's Eve at midnight. Las Vegas prepared to host hundreds of thousands of partiers on the Strip with rooftop fireworks and celebrity-studded parties at nightclubs. Miami has its own fruit, The Big Orange, a neon citrus with a new animated face that will rise up the side of a downtown hotel as fireworks go off nearby.
In Europe, around 80,000 partygoers at the Hogmanay street party in Edinburgh were welcoming 2012 at the stroke of midnight before erupting into a mass rendition of Auld Lang Syne. In London, some 250,000 people gathered to listen to Big Ben chime at the stroke of midnight during London's scaled-back New Year's celebrations. Fireworks are set off from the London Eye, the giant wheel on the south bank of the river.
Revelers in Spain greeted 2012 by eating 12 grapes in time with Madrid's central Puerta del Sol clock, a national tradition observed by millions who stop parties to follow the chimes on television.
Tens of thousands of young people in the Spanish capital gathered at six indoor "macro-parties" the city council had authorized in big venues such as the city's main sports hall.
Milena Quiroga was to be among the many there happy to move on. "I am glad to see 2011 go because it was a tough year; my restaurant laid off almost half of the staff," said the 25-year-old waitress.
The mood was festive in the South Pacific island nation of Samoa, where, for once, revelers were the first in the world to welcome the new year, rather than the last.
Samoa and neighboring Tokelau hopped across the international date line at midnight on Thursday, skipping Friday and moving instantly to Saturday. The time-jump revelry that began at 12:01 a.m. on Dec. 31 spilled into the night.
Samoa and Tokelau lie near the dateline that zigzags vertically through the Pacific Ocean; both sets of islands decided to realign themselves this year from the Americas side of the line to the Asia side to be more in tune with key trading partners.
In Europe, suffering an unprecedented economic crisis that has put the euro's existence in question, officials promised no reprieve for 2012.
"A very difficult year is coming," said Greece Prime Minister Lucas Papademos, whose government has imposed especially harsh austerity measures. "We must continue our effort decisively. So that our sacrifices will not have been in vain."
In light of the warning, Nicholas Adamopoulos, who works as a manager at a pharmaceuticals company, couldn't muster a sunny outlook for the new year.
"You want optimistic people, you go to Brazil," he said.
Associated Press writers Kristen Gelineau in Sydney, Harold Heckle in Madrid, Meera Selva in London, Melissa Eddy in Berlin, Lynn Berry in Moscow, Ray Lilley in Wellington, New Zealand, Teresa Cerojano in Manila, Philippines, Kelvin Chan in Hong Kong, Dorie Turner in Atlanta and David B. Caruso and Chris Hawley in New York contributed to this report.