Sydney as always was one of the first major cities in the world to usher in the new year amid frenzied fanfare and spectacular fireworks.
Three hours before midnight, a 9-minute firework display was launched from the bridge deck and barges across the Sydney Harbor as a preliminary event for young children.
The pyrotechnics display consisted of around 11,000 shells, 100,000 individual effects and 25,000 shooting comets at a cost of $6.06m, according to organisers.
They also estimated that as many as a billion people around the world would have watched the display that was accompanied by live music.
New Zealanders welcomed 2015 with a giant clock on Auckland's landmark Sky Tower counting down the minutes until the New Year.
A huge fireworks display was then launched from the top of the tower at midnight.
On the opposite side of the world, United States' New York city will drop its Waterford crystal ball at midnight, in a tradition being increasingly copied across the US with twists celebrating local icons.
Amid the celebrations, some US cities were also on alert for protests related to recent police killings of unarmed black men.
No plans for major protests were announced in New York, where the police department is still mourning two officers shot to death in a patrol car. But security will be tight, with more personnel than usual.