London's Big Ben was at the heart of the capital's Big Bang last night as a spectacular fireworks display welcomed in 2012.
The iconic landmark made sure the Olympic year was welcomed in style in a stunning display that saw fireworks launched from the tower at midnight.
In a first for the London's New Year celebrations, the pyrotechnics were fired from the clock to coincide with each strike of the bell, marking the start of 2012.
There was a distinctly Olympian theme to the display on the River Thames with fireworks launched over the London Eye in the shape and colours of the Olympic rings. The accompanying soundtrack saw Chariots of Fire kick off a medley of London-themed songs.
Mayor of London Boris Johnson said: "Our New Year fireworks were a brilliant start to a spectacular year.
"This is just the beginning - as the eyes of the world turn to London for the Olympic and Paralympic Games, there will be amazing events across the capital up to, during and beyond a summer like no other."
About 250,000 people were estimated to be in the capital to watch the 11-minute and 15-second display, which saw 50,000 projectiles light up the capital's skies.
The Mayor of London's office said the display was the result of 12 months of planning. A crew of 306 has been working on the site since Boxing Day, with 1,803 staff - including stewards - on duty on the night itself.
There were 30 tonnes of equipment on the three fireworks barges on the river ready for the display, which was triggered by GPS to the chimes of Big Ben.
Scotland Yard said it had 3,000 officers on duty both at street level and on podiums to give them a bird's-eye view of any troublemakers in the crowds.
Revellers had travelled to London from around the world to welcome in 2012 and were thrilled by the dazzling display.
Horst Ritter, 41, an IT worker from Frankfurt, Germany, said: "It was really fantastic, it was better than expectations. Absolutely a great start to 2012.
"The weather was fine and everything was perfect. Thank you to London for the great fireworks."
Amy Malan, 32, a housewife from California, said: "It was one of the best displays we have ever seen. It was more than we expected, so amazing.
"It was such a brilliant start to 2012, they were just never-ending, so great."
Nathan Akpoteni, 20, a student from Croydon, south London, said: "It was absolutely amazing, once in a lifetime.
"It's just exhilarating being here. Watching it on TV is one thing. Actually being here, taking it in with the ambience, is wonderful.
"You really get the essence of London. It's really started the new year with a bang. This is what we want to do to kick off an Olympic year."
Big crowds were also seen in other cities, including in Edinburgh for the Hogmanay street party attended by some 80,000 people.
In Cardiff, meanwhile, the annual Calennig celebrations also featured a fireworks display.
But in Manchester city centre the planned fireworks were cancelled due to a lack of a sponsor.
Earlier in Sydney, glittering fireworks in the shapes of butterflies, hearts and a cascading waterfall exploded over Sydney's Harbour Bridge as cheering revellers welcomed 2012.
More than 1.5 million people crowded on to yachts and along the shores of the city's harbour to watch the shimmering pyrotechnic display designed around the theme "Time to Dream".
The mood was festive on the South Pacific island of Samoa, where, for once, revellers were the first in the world to welcome the new year, rather than the last.
Samoa and neighbouring Tokelau hopped across the international date line at midnight on Thursday, skipping Friday and moving instantly to Saturday. The time-jump revelry that began at 12.01am on December 31 spilled into the night, with Samoans and tourists crowding around pools and on beaches to toast the start of 2012.
Things were slightly more subdued in New Zealand, where torrential rain and thunderstorms forced fireworks displays in the capital, Wellington, the North Island city of Palmerston North and at the popular Mount Maunganui beach area to be cancelled.
Aucklanders had better luck, with thousands crowding the city to watch fireworks erupt from the Sky Tower.
In Brazil, heavy rains did not halt parties as upward of two million people gathered on Copacabana beach in Rio de Janeiro and nearly as many on a main avenue in Sao Paulo, South America's biggest city. Massive fireworks displays and top music acts graced stages across the nation.
From Athens to Malaysia, crowds gathered on New Year's Eve in front of iconic landmarks to watch fireworks displays.