Turkish police have arrested two suspected members of the self-proclaimed Islamic State over an alleged plot to attack New Year's Eve celebrations in the capital Ankara.
Meanwhile, in Bali, more than 9,000 police will be on New Year's Eve duty after a recent alert from the Australian Federal Police helped lead to several arrests in Indonesia.
And around the world, security officials are on high alert in major cities as people make their way to New Year's Eve celebrations.
Julia Calixto reports.
The countdown is on once again, with final preparations underway for New Year's Eve celebrations across the globe.
But at the end of a tumultuous year, the focus for many organisers is on security.
In Paris, city officials say the New Year will be welcomed in a spirit of "sobriety and togetherness."
Instead of the city's usual fireworks display, images will be projected onto the Arc de Triomphe and broadcast on big screens along the Champs Elysee.
French defence minister Jean-Yves Le Drian has stressed the need for special vigilance after the November attacks in the city that left 130 dead and hundreds injured.
(Translated) "I think that there have never been as many police and army protecting the French people. This operation, Sentinel, is paramount for our troops, more important than our operations in Mali, Central African Republic or the Middle East. But it is the same fight."
About 60,000 police and soldiers have been deployed across France over the New Year period.
Despite security concerns, thousands are expected to turn up to the event, including many overseas tourists.
Mexican tourist Manuel Torres is one attending.
"We're not really scared about it. We want to enjoy it. We've never been here on New Year's Eve, and it's magical. I think we don't need to worry about it."
British tourist Mark Scarrott says he is pleased with the extra security in Paris but admits the November attacks have left him a little uneasy.
"Obviously, New Year's Eve will be a little bit different for this city. I don't think we will be heading out into the main attractions, just because of the things that have happened. But, generally, in the days and the nights, we do feel safe enough."
Authorities across the world have been put on alert for possible IS attacks.
Turkish police detained two people linked to the group who were allegedly plotting an attack on celebrations in the capital Ankara.
Brussels announced it has cancelled its New Year's festivities over a terrorism alert.
Earlier in the week, police there arrested two people suspected of planning attacks during the festive season.
In Indonesia, another two arrests have been made in connection with an alleged plot to send suicide bombers to New Year's Eve celebrations in Jakarta.
More than 9,000 police will be patrolling Bali on New Year's Eve, focusing on tourist areas where such attacks happened previously.
Police in Bali have been placed on the highest alert level.
In London, Metropolitan Police Superintendent Jo Edwards says there are no specific threats directed at celebrations in the city but the policing plan is in constant review.
"The public will probably see an increased number of police officers, and that will include firearms officers, that will include City of London officers. And British Transport Police have their own policing plan at transport hubs, which will also include firearms officers. So the aim of the plan is to provide a strong, proportionate response and to reassure people so they can come into London and enjoy the festivities."
In New York's Times Square, about 6,000 officers will be on patrol for the iconic drop of the ball at midnight.
New York Police Department Commissioner Bill Bratton says there are currently no known threats involving the event.
"We are not aware of any threat at this time that we deem credible, and we have a constant threat analysis stream that we are constantly reviewing. But, again, we are not aware of any threat at this time that we deem credible to this event here in Times Square."
An estimated 1 million people are expected to attend the event, which began in 1907 and has been cancelled only during wartime blackouts.
And in Sydney, more than 1.6 million people are expected to flock to Sydney's Central Business District for the largest New Year's Eve gathering in the country.
Police and paramedics are expected to be out in force.
