After a year in which the British capital hosted the Olympic and Paralympic Games, plus the showpiece events of Queen Elizabeth II's diamond jubilee celebrating her 60 years on the throne, the chimes of Big Ben turned the clock on 2012 at 0000 GMT.
That was the cue for a dazzling pyrotechnics display centred on the London Eye observation wheel, with up to 250 000 people thought to be lining the riverbanks for a glimpse of the free 11-minute salvo.
As the fireworks exploded, the words of London Games chairperson Sebastian Coe from the Olympic closing ceremony rang out across the Thames, saying: "We lit the flame and we lit up the world".
The best viewing areas along the riverbanks filled up hours in advance, and revellers heartily counted down the clock to 2013. "What an amazing end to an incredible year," said London Mayor Boris Johnson. "Watched by hundreds of thousands in the capital and millions around the globe, London has proved, yet again, that it can pull off spectacular world-class events in style.
"As we welcomed the world to the magnificent celebrations for the Queen's diamond jubilee and the glorious success of the Olympic and Paralympic Games, London was at its very best.
"It's been a wonderful year, but believe me, 2013 is going to be every bit as exciting."
After the salvo of 12 500 fireworks, a giant cloud of smoke drifted eastwards downstream towards Greenwich, through which the world's prime meridian passes and where Greenwich Mean Time takes its name from.
Across the capital, smaller fireworks displays could be seen out towards suburbs like Wimbledon. London Underground trains were running throughout the night to help party-goers get home.
Meanwhile in Edinburgh, thousands of revellers danced on the city streets for its Hogmanay new year party. Around 75 000 party-goers counted down the last 10 seconds of 2012 before joining in a mass rendition of the traditional tune Auld Lang Syne after the clock struck midnight in the Scottish capital.
The five-minute fireworks display from the ramparts of Edinburgh Castle was set to music for the first time. Simple Minds headlined concerts across five stages.
Tickets for the celebrations were bought by people in more than 60 countries, including Australia, Brazil, Japan and the United States. – Sapa-AFP