New Year arrived first in the South Pacific. At midnight local time (1100 GMT) fireworks were set off over Auckland's Sky Tower in New Zealand.
Spectacular displays were also enjoyed in London and Paris and other capital cities across Europe. Further west, Brazil has marked the New Year, and hundreds of thousands who packed New York's Times Square were showered with confetti at midnight.
Las Vegas welcomed 2010 with an estimated 315,000 revellers and fireworks from casino rooftops.
World leaders have spoken of their hope for 2010 compared with the difficulties many countries faced in 2009.
The Japanese capital, Tokyo, greeted the new year in traditional style, with bells rung in temples at midnight.
Thousands of people in Beijing gathered in a shopping centre to mark the change of the Lunar New Year.
Despite heavy snowfall and temperatures down to -10C (14F), more than 120,000 Russians were on Red Square in Moscow to see fireworks and hear President Dmitry Medvedev congratulate them on "bearing up" over the past year.
In the French capital, Paris, the Eiffel Tower was illuminated by a pulsating, multi-colour display, described by city officials as "a giant Christmas tree with tinsel".
London's spectacular firework display - which began on the final chimes of Big Ben - centred on the huge London Eye wheel on the banks of the River Thames.
In Venice, revellers rang in 2010 with wet feet because of a high tide at midnight.
As the US celebrated, security was tight in New York's Times Square, with partygoers banned from taking rucksacks or large bags into the area.