A look at how people around the world are ringing in 2018:
Fireworks lit up the sky above Sydney Harbour, highlighting the city's New Year's celebrations.
The massive fireworks display included a rainbow waterfall cascade of lights and color flowing off the harbor's bridge to celebrate recently passed legislation legalizing gay marriage in Australia.
Over a million people were expected to gather to watch the festivities. Security was tight, but officials said there was no particular alert.
Sydney officials said the event would generate some $170 million for the city and "priceless publicity." Nearly half the revelers were tourists.
Tens of thousands of New Zealanders took to streets and beaches, becoming among the first in the world to usher in 2018.
As the new year dawned in this southern hemisphere nation, fireworks boomed and crackled above city centers and harbors, and party-goers sang, hugged, danced and kissed.
In Auckland, New Zealand's biggest city, tens of thousands gathered around Sky Tower as five minutes of nonstop pyrotechnics exploded from the top of the structure.
But on nearby Waiheke Island, 30 kilometers (20 miles) away, authorities canceled the planned fireworks display because of drought conditions and low water supplies for firefighters.
Those willing to brave the cold in Beijing will join a countdown at the tower at Yongdingmen Gate, a rebuilt version of the Ming dynasty-era landmark gate at the southern end of the city's north-south axis.
Bells will be rung and prayers offered at temples in Beijing, but the Gregorian calendar's New Year's celebrations are typically muted in China compared to the Lunar New Year, or Spring Festival, a time of fireworks, feasts and family reunions.
Authorities throughout China are also on high alert for stampedes or terror attacks at large public gatherings. Police in the central city of Zhengzhou are putting 3,500 officers on duty across the city while residents gather to watch a light show and cultural performance in a public square.
The official Xinhua News Agency reported that President Xi Jinping sent a New Year's greeting to his Russian counterpart, Vladimir Putin, saying Beijing is ready to boost cooperation with Russia in 2018.
Many Japanese are celebrating the arrival of the Year of the Dog in the traditional way of praying for peace and good fortune at neighborhood Shinto shrines, and eating New Year's food such as noodles, shrimp and sweet black beans.
Barbecued beef and octopus dumpling stalls were out at Tokyo's Zojoji Temple, where people take turns striking the giant bell 108 times at midnight, an annual practice repeated at other Buddhist temples throughout Japan.
North Korea's nuclear and missile programs cast a shadow over Japan's hopes for peace, said 33-year-old cab driver Masaru Eguchi, who was ready to be busy all night shuttling shrine visitors.
"The world situation has grown so complex," Eguchi said, adding that he also worried about possible terrorism targeting Japan. "I feel this very abstracted sense of uncertainty, although I really have no idea what might happen."
After spending an exhausting year that saw a presidency toppled by a corruption scandal and nuclear-armed North Korea firing missile after missile, South Koreans enter 2018 in need of a happy distraction. The upcoming winter Olympics just might do it.
Thousands of people are expected to fill the streets near Seoul's City Hall for a traditional bell-tolling ceremony to usher in the new year. The group of dignitaries picked to ring the old Bosingak bell at midnight includes Soohorang and Bandabi — the tiger and bear mascots for the Pyeongchang Winter Games and Paralympics in February and March.
Tens of thousands of people are expected to flock to eastern coastal areas, including Gangneung, the seaside city that will host the Olympic skating and hockey events, to watch the sun rise on 2018.
Security was tight in the southern Indian city of Bangalore to prevent a repeat of incidents of alleged groping and molestation of several women during last year's New Year's Eve celebrations.
Sunil Kumar, the city's police commissioner, said at least 15,000 police officers were on duty and were being aided by drones and additional closed-circuit television cameras.
Last year, police first denied that any sexual harassment had taken place during the celebrations in Bangalore, India's information technology hub. But later, police detained at least six men after several video clips of women being attacked by groups of men spread on social media.
Hours before midnight, authorities had already reported that at least 86 people had been injured by celebratory firecrackers in the Philippines, which has some of the most raucous New Year's celebrations in Asia.
Although the number of injuries has tapered off in recent years, largely due to hard economic times and government scare campaigns, the figures remain alarming. President Rodrigo Duterte signed an order in June confining the use of firecrackers to community-designated areas, such as near shopping malls and parks.
Many Filipinos, largely influenced by Chinese tradition, believe that noisy New Year's celebrations drive away evil and misfortune. But they have carried that superstition to extremes, exploding dangerously large firecrackers and firing guns to welcome the new year despite threats of arrest.
Security measures were ramped up across Turkey, which was hit by a New Year's attack a year ago that killed dozens.
In Istanbul alone, 37,000 officers were on duty, with multiple streets closed to traffic and large vehicles barred from entering certain districts. Several New Year's Eve street parties were canceled for security reasons.
Early on Jan. 1, 2017, an assailant shot his way into Istanbul's Reina nightclub, where hundreds were celebrating New Year's. Thirty-nine people were killed — mostly foreigners — and 79 wounded. The Islamic State group claimed responsibility.
On Sunday, some 100 people gathered outside the nightclub to remember the victims of the attack.
Romanians prepared to usher in a new year in which the focus is expected to be an anti-corruption fight as the government seeks to push through legislation that critics say will make it harder to punish high-level graft.
Television stations broadcast live from supermarkets full of last-minute shoppers, while beauty salons reported full bookings as revelers geared up for traditional celebrations of copious meals that can run to hundreds of euros (dollars).
Others meditated and prayed at Orthodox churches and monasteries. In rural eastern Romania, villagers danced traditional pantomime-like jigs to welcome the new year, wrapping themselves in bear furs or dressing as horses.
In his New Year message, President Klaus Iohannis praised Romanians who staged the largest protests since the end of communism.
Tens of thousands of revelers will ring in the new year in Las Vegas under the close eye of law enforcement just three months after the deadliest mass shooting in modern U.S. history.
Tourism officials expect about 330,000 people to come to Las Vegas for the festivities, which are anchored by a roughly eight-minute fireworks display at the top of seven casino-hotels.
Acts including Bruno Mars, Britney Spears, Celine Dion and the Foo Fighters will keep partiers entertained before and after midnight at properties across Sin City.
The Las Vegas Metropolitan Police Department will have every officer working Sunday, while the Nevada National Guard is activating about 350 soldiers and airmen.
The federal government also is sending dozens of personnel to assist with intelligence and other efforts.
Revelers around the world ring in 2018, say bye to the old
A look at how people around the world are ringing in 2018: