Spectacular firework displays have lit up skies over some of the world's best-known landmarks - from the Arc de Triomphe in Paris to the Burj Khalifa in Dubai.
Here's a look at how cities across the globe have marked a brand-new decade.
Nearly 24 hours after Samoa first rang in 2020, Alaska's largest city welcomed the new decade with an organised fireworks display.
The police department wished its remote population a happy New Year by posting dramatic footage of a meteor falling to earth nearby, recently captured by a squad car's dashcam.
It invited people to make a lucky wish on the "shooting star".
While the West Coast City of Angels also celebrated in customary fashion, there was a sobering New Year message from the police for would-be partygoers.
The force warned on Twitter of the dangers posed by "celebratory gunfire".
It said: "The laws of physics say that what goes up must come down - don't let that be a bullet.
"We're all happy to ring in the New Year (and a new decade), but let's do it without putting innocent people at risk."
In Times Square, thousands of lucky revellers gathered to see the famous glitter ball drop.
Alanis Morissette, the Korean pop group BTS and rap-pop star Post Malone were among those performing in the heart of Manhattan.
On a serious note, high school science teachers and students highlighted the importance of tackling climate change as they pressed the button that begins the 2020 countdown.
A whopping 1,360kg of confetti and pyrotechnics soon followed.
Meanwhile, there were celebrations of a more personal sort when New York city firefighter Michael Terriberry used the occasion to pop the question to his now fiance, Nasstaja Zepeda.
Rio de Janeiro
There was a strong turnout at Brazil's Copacabana beach come midnight - with three million people watching a 14-minute extravaganza boasting 15,422kg of fireworks.
Music, drinks and religious rituals were held on the shore, with many following tradition and dressing in white - symbolising their hope for peace.
Many are set to stay on the beach until sunrise, when they will take their first dip of 2020 in the ocean and wash away their troubles from the year before.
In Sao Paulo, almost all of the fireworks set off were silent so pets wouldn't be bothered by the noise.
Celebrations in Germany's capital centred on the Brandenburg Gate.
In other cities, such as Munich and Hamburg, citizens were actually banned from having their own private firework displays amid concerns about the environment.
Crippling transport strikes didn't dent the party spirit in France, with upbeat Parisians using their bikes and scooters to head down to the Champs-Elysee for a firework display.
Security was tight, with police setting up a perimeter around the famous avenue. Traffic restrictions were also in force, and alcohol was banned.
Not one, not two, but seven different fireworks displays were taking place across Dubai - with hundreds of thousands gathering at the 828m (2,716ft) tall Burj Khalifa, the world's tallest building, to mark 2020's arrival.
Dubai is especially popular with tourists from Europe and Russia at this time of year as they try to escape the winter.
In an attempt to keep the massive crowds safe, police set up walkways around the Burj Khalifa for male-only groups - separating them from families and women.
Not everyone was blessed with good weather, unfortunately. In Indonesia's capital, torrential rains dampened the spirits of tens of thousands of revellers as they waited for fireworks.
Events in other areas were also affected by fears that Anak Krakatau, an active volcano, may be about to have a large eruption.
The New Year celebrations were overshadowed by recent protests, with thousands of people breaking out into pro-democracy chants shortly after midnight.
There were no fireworks this year on the neon-lit promenades of Victoria Harbour for the first time in a decade, with officials citing security concerns.
Instead, there was a light show starring the city's tallest skyscrapers - with small-scale pyrotechnics launched from rooftops along the waterfront.
In accordance with tradition, people took turns striking Buddhist temple bells to mark 2020.
This is the most important holiday in Japan - with stalls selling sweet rice wine, fried noodles and candied apples to hungry partygoers.
It's going to be a big year for the country, with all eyes on Tokyo as it prepares to host the Olympics in the summer.
It may be the capital of an isolated state, but Pyongyang remained determined to welcome in a new decade in style.
Fireworks lit up the North Korean city as 2020 began. Over in neighbouring South Korea, a traditional bell-tolling ceremony took place on the cold streets of Seoul.
Celebrations in Australia were clouded by the recent deadly wildfires across the country, with officials in Sydney deciding to press ahead with their multimillion-dollar display.
There had been calls for the event to be cancelled in solidarity with fire-hit areas of New South Wales, but the city's mayor said planning had begun 15 months ago, the event had already been paid for, and it would give a boost to the economy.
Elsewhere in Australia, several towns in the east cancelled their celebrations altogether as naval vessels and military helicopters helped firefighters rescue those fleeing the fires.
Among the first to celebrate the New Year were cities in New Zealand - some 13 hours before London.
After a challenging year, a dramatic pyrotechnic display in Auckland - featuring half a tonne of fireworks - gave thousands of people a well-deserved opportunity to get into the party spirit.