Revelers welcome 2018 in South America

Millions gathered on Brazil's Copacabana beach late Sunday to welcome 2018 in sultry conditions -- while a frigid North America prepared to close out the world's New Year celebrations.

A chilly Europe had already said goodbye to 2017, and the other side of the globe in Hong Kong and Sydney -- where major celebrations began hours earlier -- was already nursing a January 1st hangover after partying with dazzling firework displays.

The traditional pyrotechnics on Rio de Janeiro's beachfront got an extra blast this year, with a performance by Brazilian singer Anitta who gained worldwide recognition through a video of her in a mini-bikini performing "Vai Malandra" ("Come on bad girl").

"I am preparing a special show for you," she said on Twitter.

An NYPD officer K-9 unit patrols during New Year's Eve celebrations in Times Square

Bikinis were the last thing on the minds of North American revelers, who would follow Rio and South America in welcoming the New Year.

Much of the United States and Canada is bundled up to cope with unusually cold weather, including the roughly two million people gathered at New York's Times Square under the tightest security in years.

Most dressed in thick coats and snow gear, braced for a night tipped to be the coldest since 1962 -- with temperatures of -10 C (14 F).

Hader Ghulam, 27, a Pakistani student based in Oklahoma, told AFP he was ready for the cold, and felt "pretty safe" given all the security measures.

Tightest security in years

In London more than 100,000 ticket-holders gazed up at a spectacular pyrotechnics display from the banks of the River Thames, before dancing to "Auld Lang Syne."

Keeping with tradition, the Big Ben bell in the Houses of Parliament rang in Britain's new year. Although the clock tower is undergoing renovations, the chimes were turned back on especially for the celebrations.

In London more than 100,000 ticket-holders watched a spectacular pyrotechnics display from the banks of the River Thames, before dancing to Auld Lang Syne 

In Britain, despite the capital being hit by four terror attacks in 2017, Scotland Yard said it had fewer police officers on the streets of London than during last year's event.

Meanwhile, tens of thousands of people had been expected in Edinburgh for its Hogmanay celebrations -- one of the world's biggest street parties.

Other European cities were similarly awash with people despite the winter cold.

In Paris hundreds of thousands of partygoers braved a storm warning and drizzle to line the Champs-Elysees avenue before a dazzling light show and a fireworks display lit up the Arc de Triomphe.

Nearly 2,000 security forces were deployed to protect the crowd -- out of about 140,000 mobilized nationwide to guard against the jihadist threat which authorities describe as "still high".

"Life goes on and they (jihadists) are on the retreat," said one reveler, who gave his name only as Stephane.

In Berlin, special tents were set up at the Brandenburg Gate to assist female victims of sexual harassment, following mass assaults on women in Cologne two years ago.

Hong Kong's famous harbour is lit up by fireworks as the city celebrates the arrival of 2018

In Cologne itself, 1,400 police were mobilized, street lighting was improved and more video cameras were installed.

As the midnight chimes neared in western Europe, Hong Kong had already moved into 2018 with a stunning fireworks display over Victoria Harbor. Thousands watched as "shooting stars" were fired from the rooftops of skyscrapers during a musical spectacular.

Around the world

Three hours earlier Australia had rung in the New Year with a magnificent show of rainbow-colored fireworks cascading from Sydney Harbor Bridge.

Partygoers marked the nation's legalization of gay marriage, but under tight security -- a focus around the world due to fears that crowds could be targets for vehicle and other terror attacks.

Sydney kicked off New Year's Eve celebrations around the world with rainbow-themed fireworks hailing the legalisation of same sex marriage

The stronger police presence included some officers carrying semi-automatic rifles in Sydney and bollard barriers against vehicles. Earlier in December, one man was killed and more than a dozen hurt when a man ploughed a car into a crowd of pedestrians in Melbourne.

Elsewhere, Dubai celebrated with a laser show on the world's tallest tower, the 828-metre (2,716-foot) Burj Khalifa.

Moscow likewise entered the new year with major boulevards and 36 key sites decked out.

In Africa, Cameroon President Paul Biya used the occasion to remind his citizens of their "duty" to "maintain republican order" as well as "social peace and national unity" amid unrest in the country's Anglophone regions.

In a year-end speech, Gabon's President Ali Bongo vowed "radical change in governance" for the country where around a third of the population lives below the poverty line.

Looking ahead to 2018

The Islamic State group's defeat in Iraq and Syria was one of the year's major stories in 2017, but jihadists remain a threat.

Donald Trump stole the news spotlight after making his debut as US President last January, with his "America first" policies and a bombastic personal style that has shaken up international diplomacy.

Revellers celebrate New Year on the beach in Zanzibar, Tanzania

"2018 will be a great year for America!" Trump said in a tweet to close out the year.

Political and diplomatic earthquakes set to rumble into 2018 include the Middle East crisis between Saudi Arabia and its allies against Qatar, and the humanitarian disaster in Yemen.

In Europe, further talks on Brexit will help shape the region's future trade relationship while Russia is set to host the football World Cup amid frictions with the West.

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