Here's a look at how people are ushering in the new year:
The Pacific island nation of Kiribati was the first in the world to welcome the new year, greeting 2019 with muted celebrations after spending 2018 on the front line of the battle against climate change.
Kiribati is made up of low-lying atolls along the equator which intersect three time zones, the first of which sees the new year 14 hours before midnight in London.
Much of the nation's land mass, occupied by 110,000 people, is endangered by rising seas which have inundated coastal villages. The rising oceans have turned fresh water sources brackish, imperiling communities and raising doubts the nation will exist at the next New Year. Former President Anote Tong said the only future for Kiribati may be mass migration.
The new year was welcomed in the capital, Tarawa, with church services and mostly quiet private celebrations.
In Auckland, New Zealand's biggest city, tens of thousands gathered around Sky Tower as fireworks exploded from the top of the 328-meter (1,076-foot) structure. Across the southern hemisphere nation, thousands took to beaches and streets, becoming the first major nation in the world to usher in 2019.
Fireworks boomed and crackled above city centers and harbors.
A thunderstorm drenched tens of thousands of people as they gathered for Sydney's traditional spectacular fireworks display, creating a show of its own with dozens of lightning strikes.
Police estimated that more than a million people would crowd Sydney Harbor to view the glittering fireworks. People began gathering early in the day at popular vantage points, including the Opera House and the ends of the Harbor Bridge.
The show was to feature more than 100,000 pyrotechnic effects accompanied by music culminating at midnight with "(You Make Me Feel Like) A Natural Woman," made famous by Aretha Franklin, who died in August.
Police said they were taking precautions to prevent any terrorist attack, but assured revelers there was no specific threat.
"We put obstacles between those large crowds and vehicles to ensure people can get in and out safely and enjoy their night in safety," police Acting Deputy Commissioner Mark Walton said.
More than 1 billion people around the world were expected to watch the fireworks on television.
THE UNITED NATIONS
U.N. Secretary-General Antonio Guterres issued a bleak New Year's message that called climate change an existential threat and warned that "it's time to seize our last best chance." He noted growing intolerance, geo-political divisions and inequality, resulting in people "questioning a world in which a handful of people hold the same wealth as half of humanity."
"But there are also reasons for hope," he said. "As we begin this New Year, let's resolve to confront threats, defend human dignity and build a better future - together."
After an eventful year that saw three inter-Korean summits and the easing of tensions over North Korea's nuclear program, South Koreans enter 2019 with hopes that the hard-won detente will expand into a stable peace.
Thousands of South Koreans were expected to fill the streets of the capital, Seoul, for a traditional bell-tolling ceremony near City Hall to usher in the new year. Dignitaries picked to ring the old Bosingak bell at midnight include famous surgeon Lee Guk-jong, who successfully operated on a North Korean soldier who escaped to South Korea in 2017 in a hail of bullets fired by his comrades.
Elsewhere, about 10,000 people were expected to attend the tolling of a "peace bell" at Imjingak, a pavilion near the border with North Korea.
Leader Kim Jong Un will keep North Korea watchers busy on New Year's Day, when he is expected to give his annual address laying out the country's priorities for the year ahead. The speech is often the best gauge of what the North Korean leadership is focused on and what tone it will take in its dealings with the outside world.
Kim's speech it will be parsed carefully for clues about his thinking on denuclearization talks with Washington and a second summit with President Donald Trump, relations with South Korea, and North Korea's efforts to get out from under international sanctions as it tries to build its domestic economy.
In his New Year's speech this past year, Kim proposed talks with South Korea to reduce tensions and said the North would be willing to participate in South Korea's Winter Olympics, setting off a series of summits with the South and the U.S.
New Year's Eve isn't celebrated that widely in mainland China, where the lunar New Year in February is a more important holiday, but countdown events were being held in major cities and some of the faithful headed to Buddhist temples for bell-ringing and prayers.
The city of Beijing was holding a gala with VIP guests at the main site of the 2008 Summer Olympics. The event looked ahead to the 2022 Winter Games, which also will be held in the Chinese capital.
Additional police were deployed in parts of Shanghai, where a New Year's Eve stampede in 2014 killed 36 people. In Beijing, outdoor revelers had to brave temperatures well below freezing.
President Xi Jingping, in a message broadcast at the top of the evening news, outlined the country's achievements over the past year and said that by hosting a series of multinational meetings in 2018, "we have put forward China's proposals and sent out China's voice."
In Hong Kong, festive lights on the city's iconic skyscrapers provided the backdrop for a fireworks, music and light show over Victoria Harbor on a chilly evening. About 300,000 people were expected to line the waterfront.
While many celebrate New Year's Eve with fireworks, hundreds of Thais traveled to Takien Temple in a suburb of Bangkok to lie inside coffins for traditional funeral rituals. Participants believe the ceremony - symbolizing death and rebirth - helps rid them of bad luck and allows them to be born again for a fresh start in the new year.
Participants held flowers and incense in their hands as monks covered them with pink sheets and chanted prayers for the dead.
"It wasn't scary or anything. It is our belief that it will help us get rid of bad luck and bring good fortune to our life," said Busaba Yookong, who came to the temple with her family.
Bangkok is filled with modern glitzy malls and high-rise buildings, but superstitious beliefs still hold sway in many aspects of Thai society.
Suspected Muslim militants remotely detonated a bomb near the entrance of a mall in the southern Philippines as people did last-minute shopping ahead of New Year's Eve celebrations, killing at least two and wounding nearly 30, officials said.
The bomb went off near a baggage counter at the entrance of the South Seas mall in Cotabato city, wounding shoppers, vendors and commuters. Authorities recovered another unexploded bomb nearby as government forces imposed a security lockdown in the city, military and police officials said.
The bombing is the latest in a number of attacks blamed on militants in the volatile region.
NEW YORK CITY
Snoop Dogg, Sting and Christina Aguilera will welcome 2019 in a packed Times Square along with revelers from around the world who come to see the traditional crystal ball drop.
Spectators are expected to start assembling early in the afternoon for the made-for-TV extravaganza. The celebration will take place under tight security, with partygoers checked for weapons and then herded into pens, ringed by metal barricades, where they wait for the stroke of midnight.