In Australia, about 1.5 million people crowded the Sydney Harbour foreshore to watch a vast array of fireworks burst into the night sky at midnight, launched from the iconic Sydney Harbour Bridge and four barges on the water.
Thousands of people also crammed into Hong Kong's harbour, where 9,000 fireworks were unleashed from the city's tallest skyscraper as well as other buildings in a display that lasted nearly five minutes.
Such spectacles were banned in Thailand, after fireworks caused a New Year's Eve blaze at a Bangkok nightclub a year ago killing 65 people.
In New York city's Times Square, hundreds of thousands gathered to celebrate despite heavy rains, slushy streets and tight security.
In Paris, about 70,000 people gathered near the Eiffel Tower for a multicoloured light show, while more than 8,000 police were deployed across the city and suburbs.
Pope Benedict XVI, in traditional prayers in St Peter's Basilica on the last day of 2009, called on Christians across the world to help families affected by the economic downturn and unemployment.
In Spain, which took over the rotating presidency of the European Union at midnight, thousands of people attended a light and sound show at the central Puerta del Sol square where a giant image of the EU flag was projected onto a building.
"This is the best street party in the world. Now I am going to work on my first hangover of 2010," Gerry Shalloe, a 32-year-old English teacher from Ireland who lives in Madrid and who attended the countdown with friends, said.
In Poland, some 90,000 people brought in the New Year at a concert in Warsaw in memory of Michael Jackson attended by the late singer's sister La Toya.
In Pakistan, spirits were dampened in the city of Karachi by a deadly suicide attack during a holy Shia Muslim ceremony on Monday that killed 43 people.
In neighbouring Afghanistan, soldiers maintained their alert after two deadly attacks claimed the lives of seven CIA agents and five Canadians, while two French journalists were reported kidnapped by Taliban.