Spectacular fireworks lit up the night sky in Australia as 1.5 million people flocked to Sydney Harbour to watch the display and to celebrate the New Year.
People gathered at mass at vantage points along the harbour to watch the show that has the arch of the bridge as its focal point.
This year's theme was 'Time to Dream' and it is hoped it will help inspire those who have had a particularly bad 2011 to look forward to the year ahead.
Some of the fireworks exploded into shapes of clouds - because every one has a silver lining - and a series of colourful lights were beamed into the centre of the bridge forming an 'endless rainbow'.
Time to Dream: Fireworks in Sydney Australia light up the skyline over Harbour Bridge and the Sydney Opera House
Thousands of people gathered in Sydney to watch the impressive display as Australia welcomed in the New Year
The New Year's Eve party on the island of Samoa started a whole day earlier than normal after the South Pacific nation moved 24 hours into the future, making it the first to see in the new year.
People began celebrating as soon as the clocked ticked over from Thursday, December 29, skipping Friday and moving straight onto Saturday, December 31 at 12.01am.
Samao and neighbouring Tokelau lie near the date line in the Pacific Ocean and both islands decided to realign themselves from the Americas side to the Asia side in order to be more in line with major trading partners. It is hoped the move will help improve the economy.
Pools and beaches have been packed with Samoans and tourists who are keen to be the first to celebrate rather than the last.
Elsewhere across globe millions of people are preparing to say goodbye to a year that saw mass uprisings in several Arab countries, the deaths of Osama Bin Laden, Muammar Gaddafi and Kim Jong-il.
It was also a year of economic turmoil which saw an endless string of natural disasters that devastated several countries across the world.
In Australia people gathered on the shores of Sydney's harbour to watch the iconic fireworks display over the Harbour Bridge.
The theme for this year's fireworks, top and below, is Time to Dream, in the hope it will inspire people who have had a particularly bad 2011
In London a dazzling fireworks display is expected to attract up to 250,000 people.
The London Eye will be the focal point for the pyrotechnics, which London Mayor Boris Johnson said would be a fitting way to mark the start of an extraordinary year for the city.
There will be some 12,000 fireworks, producing 50,000 projectiles, launched during the display, which is triggered by Big Ben's chimes and lasts for 11 minutes and 15 seconds.
People from across the world started to gather at the Sydney Opera House early on Saturday afternoon to watch the celebrations and get to see a 9pm preview show before the real celebrations begin at midnight
Mr Johnson said: 'A glittering display will light up the sky to herald the start of 2012, the most extraordinary and exciting year we are likely to see in our lifetime in this city.
'We will stage an incredible Olympic and Paralympic Games, which will put us in the global spotlight and spur the long-term rejuvenation of east London and bring benefits to the whole capital.
'From the magic of the Games, to the Diamond Jubilee, and the London 2012 Festival to our own outdoor arts festival, we will welcome the world with thrilling events in every corner of the capital, to create a summer like no other.'
The colourful fireworks light up the Sydney Opera House. A rainbow can be seen lighting up the Harbour Bridge in the background
Describing the planned show, a spokesman from the Mayor of London's office said: 'Without wanting to give too much away, it describes London: diverse, quirky, surprising, evolving, inspirational.
'There is a nod to the nostalgic past, but, like the city, it is very contemporary and of course it looks ahead to an amazing year for the capital.'
London-themed songs will accompany the fireworks, which are expected to be watched on television by millions of people around the world.
Those travelling to the Southbank to see the pyrotechnics have been warned that visibility may not be good.
Gareth Harvey, a weather forecaster said: 'It looks like it will be cloudy on the night but temperatures should remain mild, with the chance of a few spots of drizzle.'
Samoans celebrated New Year's Eve first this year, left, rather than last, after they skipped Friday altogether and a woman, right, celebrates in Sydney
Indian students in Ahmadabad show off placards as they prepare to welcome in the New Year
Some 3,000 police officers will be on duty overnight to deal with the crowds expected to descend on the capital, not only on the banks of the Thames to watch the fireworks but also in Trafalgar Square.
Some will be stationed on podiums to give them a bird's-eye view of any troublemakers in the crowds.
Chief Superintendent Julia Pendry, of Scotland Yard, said: 'New Year's Eve is a special time of the year and we want people to enjoy it to the full.
'Make sure you look after yourself and those around you. Officers will be out and about to deter criminals and keep crowds safe.
'New Year's Eve in central London is extremely busy so do come prepared and wrap up warm, as you may have to wait to prevent overcrowding. The viewing area does fill up really quickly and each area will be closed off by the organisers once it reaches its capacity.'
She urged people to consider watching the fireworks on TV instead, as sometimes the viewing area fills up as early as 8pm.
All travel in London will be free from 11.45pm on New Year's Eve until 4.30am on New Year's Day. Road closures will be in place in the city from 4pm on December 31.
British Transport Police have advised travellers to expect queues on their journey home from the centre of London
