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 three hours before Sydney.
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, tens of thousands gathered around Sky Tower as fireworks exploded from the top of the 328m structure.
Across New Zealand, 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.
Revellers elsewhere around the world were preparing to ring in the New Year with festivities and fireworks.
In Japan, bells at Buddhist temple bells will chime 108 times - representing the number of earthly desires a person must overcome to attain nirvana - to finish the old year and welcome the new one.
During the first three days of the New Year, millions are expected to throng shrines and temples across the country to pray for happiness and prosperity.
Sticky rice cakes called mochi are a New Year speciality, but can be a health hazard, with cases of choking reported every year.
Tens of thousands of people are expected to take part in Edinburgh's Hogmanay celebrations, while tickets to London's fireworks display, the largest display in Europe, were sold out.
Germany's biggest New Year's Eve party will take place at Berlin's Brandenburg Gate, where Eagle Eye Cherry and Bonnie Tyler are among those set to perform before a laser and firework display at midnight.
In New York, security will be tight as the Big Apple expects up to two million people on Times Square for New Year's Eve celebrations culminating with the drop of a crystal ball in the final seconds of 2018.
Eleven journalists are set to press the button releasing the ball, the New York Times reported, as part of an effort to recognise the erosion of press freedoms at home and abroad.
