Revellers around the globe are bidding a weary farewell to an unsettling year filled with challenges to many of the world's most basic institutions, including politics, trade, alliances and religion.
Here's a look at how people are ushering in the new year:
An estimated million people crowded Sydney Harbour as Australia's largest city rang in the new year with a spectacular, soul-tinged fireworks celebration.
One of the most complex displays in Australia's history included gold, purple and silver fireworks pulsating to the tune of "(You Make Me Feel Like) A Natural Woman," made famous by Aretha Franklin, who died in August. The show used 8.5 tons of fireworks and featured more than 100,000 pyrotechnic effects.
Earlier, a thunderstorm drenched tens of thousands of people as they gathered for the traditional display, creating a show of its own with dozens of lightning strikes.
Police said they took precautions to prevent any terrorist attack, but assured revelers there was no specific threat.
More than 1 billion people around the world were expected to watch the fireworks on television.
In Melbourne, 14 tons of fireworks deployed on the ground and on roofs of 22 buildings produced special effects including flying dragons. In Brisbane, an estimated 85,000 people watched as fireworks exploded from five barges moored on the Brisbane River.
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 centres and harbours.
THE UNITED NATIONS
UN 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 US.
Festive lights decorated Hong Kong's iconic skyscrapers as they provided the backdrop for a fireworks, music and light show over Victoria Harbor where some 300,000 people had gathered on New Year's Eve.
New Year's Eve is not widely celebrated in mainland China, where the lunar New Year in February is a more important holiday, but countdown events were being held in most major cities, including Beijing and Shanghai 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."
A slight drizzle failed to dampen the spirit of Malaysians, who ushered in 2019 with a spectacular display of fireworks which lit up the skyline around the Petronas Twin Towers in Kuala Lumpur as the clock struck midnight.
While many celebrate New Year's Eve with fireworks, hundreds of Thais travelled to Takien Temple in a suburb of Bangkok to lie inside coffins for traditional funeral rituals. Participants believe the ceremony — symbolising 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.
Dozens of people have been injured by firecrackers ahead of New Year's Eve, when many across the Philippines set off powerful firecrackers in one of Asia's most violent celebrations despite a government scare campaign and threats of arrests.
The Department of Health said it has recorded more than 50 firecracker-caused injuries in the last 10 days, which is expected to increase overnight when Filipinos usher in 2019 with a bang. Although still a concern, the figure is significantly lower than a year ago, partly because fewer Filipinos have purchased firecrackers due to hard economic times.
Officials have urged centralised fireworks displays to discourage wild and sometimes fatal merry-making. The notorious tradition, worsened by celebratory gunfire that turned deadly, stems from a Chinese-influenced belief that noise drives away evil and misfortune.
Japanese usually welcome the New Year with a visit to a nearby temple or shrine, but some 30,000 people at Saitama Super Arena did it with Floyd Mayweather. The American boxing legend soundly defeated his opponent, Japanese kickboxer Tenshin Nasukawa, in the first round of what was billed as three rounds of entertainment with no official record, meaning both fighters still retain their undefeated tallies. "I told Tenshin to hold your head up high," Mayweather said of his advice after the bout. Nasukawa was floored three times in the first round, and although he kept getting up, teetering, his father in the corner threw in the towel.
Hundreds of thousands of Parisians and tourists are expected to gather on the famed Champs-Elysees avenue to celebrate New Year's Eve under heavy security.
Anti-government protesters from the "yellow vest" movement have issued calls on social media for "festive" demonstrations on the famed avenue.
Paris police have set up a security perimeter in the area, with bag searches, a ban on alcohol and traffic restrictions. The Interior Ministry said Sunday that the heavy security measures are needed because of a "high terrorist threat" and concerns about "non-declared protests."
President Emmanuel Macron is to give his traditional New Year address to briefly lay out his priorities for 2019, as some "yellow vest" protesters angry over high taxes and his pro-business policies plan to continue their demonstrations in coming weeks.
Before midnight, a light show illustrating the theme of brotherhood is to take place on the Arc de Triomphe monument at the top of the Champs-Elysees.
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.