Revellers have gathered at New Year events across the world to usher in the start of 2017.
Security has been increased in major cities with barriers erected around central squares in Paris, Madrid and New York in the wake of the truck attacks in Berlin and Nice.
A huge police presence was on the streets of London as spectators from almost 100 countries began to flock to the River Thames to view the spectacular pyrotechnics, which will begin painting the night sky as Big Ben strikes midnight.
London City Mayor Sadiq Khan said the mood on the streets was "upbeat", adding it was "really important we don't allow terrorists to disrupt our celebrations on this New Year's Eve".
Sydney hosted its annual fireworks spectacular to welcome in the New Year with the biggest fireworks display the Australian city has ever seen.
The Sydney Harbour Bridge was the focal point of this year's display with 20,000 fireworks erupting from the Sydney icon.
Both the New Year's Eve displays - the 9pm (local time) family fireworks and the midnight spectacular - honoured the legendary artist Prince who died in April.
The tributes were inspired by the artist's classic song Purple Rain which saw the colour purple lighting up the Harbour Bridge and explosions of gold and purple fireworks across the harbour.
Artist David Bowie was honoured with moon, star and planet Saturn fireworks that organisers said were in honour of Bowie's song Space Oddity.
Tributes were also paid to Gene Wilder which delighted Sydneysiders and visitors with a colourful Willy Wonka display during the show.
Seven tonnes of fireworks, 12,000 shells, 25,000 shooting comets and 100,000 individual pyrotechnic effects were used in this year's display, said organisers.
In Pictures: New Year Celebrations
Meanwhile, Dublin's New Year Festival continues, as part of a three day programme to welcome 2017 in the capital.
Now in its third year, the festival includes comedy, music, literary and historical events - the highlight of which is this evening's Countdown Concert at St Stephen's Green.
The event features Walking on Cars, The Blizzards and Little Hours.
As darkness fell, the Custom House became the canvas for various video and art projections as part of the Luminosity project.
Two Luminosity 4D performances took place earlier and the the projections will remain on the building throughout the evening.
Elsewhere, a collective of Irish buskers entertained revellers at Temple Bar's Meeting House Square.
A series of "pop-up" events was held at venues including the Guinness Storehouse and Croke Park.
The Dublin Circus Project is also contributing to this year's celebrations and performed at various points around the city until 6pm, including O'Connell Street, Grafton Street and Custom House Quay.
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In the US, as many as two million people, surrounded by a ring of 40-tonne sand trucks and 7,000 police, are expected to gather in New York's Times Square to watch the glittering sphere complete its midnight drop.
Even though city and federal officials say they are not aware of any credible threats, a protective perimeter of 65 sanitation trucks filled with sand, as well as about 100 other smaller vehicles, will encircle Times Square throughout the evening.
Placed in strategic positions, the "blockers" are intended to prevent a repetition of the truck attacks in Berlin and Nice earlier this year, officials said.
At 11.59pm local time, the Waterford Crystal ball will begin to slide down a pole that sits a top a building at the point where Broadway crosses Seventh Avenue. When it completes its descent at midnight, a giant "2017" sign will illuminate and a shower of fireworks with light up the sky.
Chicago, San Francisco and other big cities across the country have also put heavy security in place to protect crowds expected to gather at public fireworks displays and other "first night" events.
In Washington, where federal budget cuts have done away with traditional New Year's Eve fireworks on the National Mall, no major events were planned.
District of Columbia police declined to comment on any special security plans, saying only that events across the world are monitored for their potential impact on the US capital.
Trump in backhanded New Year greeting to 'many enemies'
US President-elect Donald Trump sent New Year's greetings to his "many enemies" in a backhanded tweet in which he gloated over his political conquests.
"Happy New Year to all, including to my many enemies and those who have fought me and lost so badly they just don't know what to do. Love!" he wrote.
The message caps a year in which he overcame long odds to vanquish 16 other Republicans vying to become the party's White House nominee.
He then upended Democrat Hillary Clinton in last month's general election - her formidable political machine and bigger campaign coffers notwithstanding - in a shock election upset.
Happy New Year to all, including to my many enemies and those who have fought me and lost so badly they just don't know what to do. Love!
— Donald J. Trump (@realDonaldTrump) December 31, 2016
Mr Trump takes the oath of office on 20 January, when he will become the 45th US president.
