Australia's largest city Sydney put on its biggest-ever fireworks display in a spectacular welcome to the New Year, kicking off a wave of celebrations for billions around the world.
A record amount of pyrotechnics as well as new fireworks effects and colours lit up the city's skyline for 12 minutes and dazzled the more than 1.5 million spectators who packed the harbour front and parks.
An earlier thunderstorm did not dampen the spirits of revellers who camped out at vantage points, some since the early hours of the morning.
To mark the international year of indigenous languages in 2019, the harbour also hosted a ceremony celebrating Aboriginal heritage that included animations projected onto the bridge's pylons.
The party atmosphere will sweep across major cities in Asia, Europe, Africa and the Americas as the clock ticks past midnight.
A strong police presence has become a key element of the festivities, to protect crowds that could be targeted in terror and vehicle attacks.
Hong Kong: Glittering fireworks will be sent skyward from five barges floating in Victoria Harbour in a 10-minute display watched by 300,000 people on the shore.
Jakarta: Hundreds of couples will tie the knot in a free mass wedding, as those in the tsunami-hit Banten province, where affected towns were popular holiday destinations, have been told to cancel party plans to show respect for the victims.
Tokyo: Japanese will flock to temples to ring in the New Year, while US boxer Floyd Mayweather Jr will take on local kickboxer Tenshin Nasukawa in a bout staged outside Tokyo.
Moscow: Concerts and light shows will be held across the city's parks and more than 1,000 ice rinks have been opened for merrymakers.
Paris: A fireworks display and sound and light show under the theme "fraternity" is set to go ahead on the Champs-Elysees despite plans for further "yellow vest" anti-government protests at the famed avenue.
Berlin: Music lovers will party at a concert at the Brandenburg Gate, but a popular German tradition of setting off fireworks to mark the occasion has been banned in some other cities over safety concerns.
London: Britain's capital will usher in the New Year by celebrating its relationship with Europe amid turmoil over the Brexit referendum vote to leave the EU, with the fireworks display at the London Eye to feature music from the continent's artists.
Edinburgh: The Scottish capital's traditional Hogmanay celebrations will also take on a pro-European theme ahead of the year in which Britain is due to exit the union.
As the world parties, many will also look forward to 2019 and wonder whether the turmoil witnessed during the previous year will spill over into the next.
The political wrangling in Westminster over Brexit was one of the key stories of this year, with a resolution yet to be reached ahead of the scheduled March 29 departure.
US President Donald Trump dominated headlines in 2018 as he ramped up his trade war with China, quit the Iran nuclear deal, moved the American embassy to Jerusalem and met his North Korean counterpart Kim Jong Un in Singapore for a historic summit.
North Korea's commitment to denuclearisation will remain a major political and security issue into next year, as will Syrian President Bashar al-Assad's reassertion of control after Trump's shock military withdrawal announcement.
The war in Yemen, which started in 2014 and has already killed about 10,000 people and left some 20 million at risk of starvation, could take a crucial turn after a ceasefire went into effect in mid-December.
Numerous countries go to the polls in 2019, with key elections in India, Afghanistan, Indonesia, South Africa, Argentina and Australia.
Major sporting events on the calendar include the Rugby World Cup in Japan, the cricket one-day international World Cup in England and the athletics World Championships in Qatar.
