New Year's celebrations have passed off mainly peacefully around the world.
Revellers were searched as they entered New York's Times Square
Despite security concerns, hundreds of thousands of people gathered at Times Square in New York for the traditional countdown to the new year.
Revellers had been greeted with metal detectors and police searches, while warplanes patrolled the skies overhead.
Elsewhere, there were incidents of bloodshed - a bomb at a concert in Indonesia's Aceh Province and a car bomb attack on a Baghdad restaurant.
At least five people were killed, all of them Iraqis, when an explosion destroyed a restaurant in the Iraqi capital.
Police say it was caused by a car bomb placed outside the restaurant, which was packed with people.
More than 30 others were wounded in the blast.
In Aceh, at least nine people were killed and more than 30 injured at a concert staged to celebrate the New Year.
A one-year-old baby and a seven-year-old boy were among the dead.
The military has blamed the blast on Aceh separatists, but they have denied any involvement.
Security was particularly high in the United States.
The Department of Homeland Security had raised the national alert status to orange - the second highest level - 10 days ago.
Only scheduled commercial flights were allowed over New York, Las Vegas, Chicago and Washington during New Year's Eve.
Manhole covers were sealed, and post boxes, rubbish bins and newspaper stands removed.
New York police began closing Times Square to traffic several hours before the nation's biggest New Year's Eve party - featuring singer Cyndi Lauper - was due to begin.
"I was a little scared, but the security here is good," said Patrycja Galanty, 18, of Brooklyn. "I trust New York."
"I feel like this is the most secure place in the world tonight," said Andy Kelleher, 39, from Dwight in Illinois.
"I had to go through three checkpoints, plus there's the helicopters in the air, the machineguns on the rooftops, dogs sniffing the subways and they actually searched us coming in."
Security was also tightened in Las Vegas, where police were planning to deploy sharpshooters on hotel-casino roofs and to close off a number of routes.
Nevada Governor Kenny Guinn said the unprecedented security levels had been prompted by intelligence "chatter" monitored by the Department of Homeland Security suggesting that six or seven cities could be targeted for attack.
"America has certainly changed and the world has changed and we have to change with that," he told CNN.
Security forces in other countries were also being extra vigilant over the festive period.
Turkey cancelled its traditional New Year celebrations in Istanbul following last month's suicide attacks, which left 62 dead.
Security concerns meant the usual evening of free concerts and festivities in central Taksim Square, which normally attracts tens of thousands of revellers, did not go ahead.
British police had about 3,000 officers overseeing the celebrations in London, but said they had no intelligence of any specific threat.
The number of revellers in Moscow's Red Square was reportedly down this year following recent bomb attacks.