Revellers converged on the beaches of Brazil, the skyscrapers of Dubai and New York's Times Square to say good riddance to a turbulent 2014 marred by terror woes, Ebola and airline disasters.
But tragedy struck in Shanghai, Baghdad was on edge and protesters in the United States planned a sobering reminder of one of the year's biggest stories.
In the worst disaster to hit one of China's showcase cities in years, 35 people were killed in a stampede during new year celebrations in downtown Shanghai, city officials said.
The deaths occurred half an hour before midnight local time at Shanghai's popular riverfront Bund area, which can be jammed with spectators for major events. Shanghai's government said another 46 people were receiving hospital treatment, including 14 who were seriously injured.
Last week the English-language Shanghai Daily reported that the annual New Year's Eve countdown on the Bund that normally attracts about 300,000 people had been cancelled, apparently because of crowd control issues. The report said a "toned-down" version of the event would be held instead but it would not be open to the public.
About one million revellers rang in the new year in Times Square, watching a giant, glittering ball drop as a ton of confetti fell, containing well wishes for the upcoming year.
They braved cold temperatures and crowded conditions to get a good view of the festivities. Some arrived more than 12 hours in advance.
Agustina Bernacchia, a tourist from Argentina, said she wanted to experience the New Year's Eve party she had always seen on TV. "It was a dream for us," she said.
The ball drop tradition is being increasingly copied across the United States with twists celebrating local icons.
Items being dropped include: a big chilli in Las Cruces, New Mexico; a replica peach in Atlanta; a musical note in Nashville, Tennessee; a large pine cone in Flagstaff, Arizona; an oversized spurred cowboy boot in Prescott, Arizona; an 80lb wedge of cheese in Plymouth, Wisconsin; and in Escanaba, in Michigan's Upper Peninsula, a replica of a pasty.
Amid the celebration, some US cities were on alert for New Year's Eve protests related to recent police killings of unarmed black men.
Activists in Boston staged a peaceful "die-in" during First Night, Boston's popular New Year's Eve celebration. Police reported no arrests or disruptions to nearby festivities.
In New York, where police are still mourning two officers shot dead in a patrol car, dozens of protesters marched in Manhattan on New Year's Eve.
The Gulf Arab emirate of Dubai was aiming to break the world record for the largest LED-illuminated facade with its spectacular display centred on the world's tallest building.
Some 70,000 LED panels around the 2,722-foot Burj Khalifa flashed coloured lights and projected images of the country's leaders when clocks there struck midnight as a massive fireworks display erupted. The celebration draws throngs of thousands of spectators every New Year's Eve.
Emaar Properties said a team from Guinness World Records monitored the preparations. Last year, Dubai won the title for the world's largest fireworks display, according to Guinness.
In Iraq's war-scarred capital Baghdad, authorities ordered a one-off lifting of the overnight curfew in force for more than a decade to allow the city's revellers to stay out late on the streets.
Traffic was unusually heavy starting shortly after sunset and authorities closed commercial streets to vehicles in the city's centre as a precaution against possible suicide bombings by militants of the Islamic State (IS) terror group.
Thousands of partiers arrived on speedboats, yachts and ferries to dance the night away on the tiny Caribbean island of Jost Van Dyke that has long hosted one of the region's biggest, most uninhibited New Year's Eve bashes.
In the British Virgin Islands, Jost Van Dyke balloons from about 300 full-time residents to about 5,000 people each New Year's Eve as throngs of barefoot, tipsy people groove to reggae bands on white sands and hop from bar to bar. The annual tradition started in the 1960s on the idyllic island - so small it did not get electricity until 1992.
"Every year it just gets bigger and bigger. People from all over travel here to get drunk, fall down and just have as much fun as they can," said Tessa Callwood, who runs a world-famous beach bar with her husband, Foxy's Tamarind Bar & Restaurant.
More than one million people were expected to flock to the golden sands of Rio de Janeiro's Copacabana beach, where two dozen artists and DJs were performing on three stages. Tourists and locals routinely party until dawn on the beach, staying awake to watch the tropical sun rise for the first time in 2015.
A massive fireworks display blasted from boats on the Atlantic Ocean lights the sky over the crowd, which traditionally dresses in all white, a Brazilian tradition to bring purification and a peaceful year. Another tradition calls for partygoers to enter the sea up to their knees and jump over seven waves shortly after the new year begins, for luck.