The New Year 2016 celebrations have kicked off in Australia and New Zealand - but London, Paris, and New York are among the cities tightening security amid fears of a terrorist attack.
Brussels has cancelled its official celebrations because of threats of an extremist attack, Paris has called off a Champs-Élysées fireworks display and Russia has closed Moscow’s Red Square.
Last December 31, 100,000 people turned out in the Belgian capital to ring in the New Year. Brussels was home to four of the radical Islamic attackers who killed 130 people in Paris on November 13.
In the UK capital thousands of police, including increased numbers of firearms officers, will be on duty as London mayor Boris Johnson's fireworks display with Unicef brings in 2016.
Metropolitan Police spokeswoman Superintendent Jo Edwards said: "Our plans are purely precautionary and not as a result of any specific intelligence."
New Zealand counted down the seconds to midnight with a giant digital clock on Auckland's Sky Tower as it become the first nation with a sizeable population to welcome in 2016.
Horns blared and crowds cheered as the tower was then lit up with fireworks, with colours shifting from green to red to white.
In Australia, officials struggling to contain the threat from home-grown extremists encouraged revellers to enjoy the evening and assured that thousands of extra police would be out patrolling the major cities.
"Don't change your way of life," Melbourne's lord mayor Robert Doyle recently urged residents of the nation's second-largest city.
People are expected to gather by the hundreds of thousands despite blistering temperatures to watch nearly 11 tons of fireworks light up the sky.
"Don't let events from around the world challenge the way that we live," he added.
Melbourne's rival, Sydney, takes seriously its position as one of the first major cities in the world to ring in each new year.
More than a million people are expected to gather along the famed harbour to watch a glittery display featuring a multi-coloured firework "waterfall" cascading off the Harbour Bridge and pyrotechnic effects in the shapes of butterflies, octopuses and flowers.
New Year's Eve is Japan's biggest holiday, and millions crammed into trains to flee the cities for their hometowns to slurp down bowls of noodles, symbolising longevity, while watching the annual Red and White NHK song competition.
As midnight approaches, families bundle up for visits to neighbourhood temples, where the ritual ringing of huge bronze bells reverberates through the chill.
Tokyo is on special alert for security issues this year, with posters in underground stations and other public spaces warning people to keep their eyes open for suspicious packages or activities.
In the Thai capital Bangkok, police-flanked partygoers will ring in the new year at the site of a deadly bombing that took place just months ago.
As the final hours of 2015 draw to a close, many are bidding a weary and wary adieu to a year marred by attacks that left nations reeling and nerves rattled.
Still, most places are forging ahead with their celebrations as many refuse to let jitters ruin the joy of the holiday.
"We still have this fear but we need to continue to live," said Parisian Myriam Oukik. "We will celebrate."
On New Year's Day, more than 8,500 performers representing 20 countries will take part in an annual parade through London. The event, which includes marching bands, cheerleaders, clowns and acrobats, kicks off in Piccadilly and finishes in Parliament Square, taking in Lower Regent Street, Pall Mall, Trafalgar Square and Whitehall.