Four riders, include an adventurer from Ireland have set off on what is described as the world's longest bicycle race.
Three, including Irish cyclist Breifne Earley, 32, started from London while another rider set off from Bangkok in a bid to break the Guinness World Record for the fastest circumnavigation of the planet.
The World Cycle Race launched from the prime meridian next to the Royal Observatory in Greenwich Park with Leitrim-born Earley setting off with L ee Fancourt, 36, from the UK and Fran Hollender, 26, from Germany.
Prasad Erande, 29, from India set off from Bangkok. The male riders are aiming to beat the record of just under 126 days and Ms Hollender is aiming for the female record of 152 days and one hour.
Organisers The Adventurists said r iders must cycle at least 18,000 miles in one direction around the planet, starting and finishing in the same location.
Mr Earley said: "I'm in it to win it but the important thing is to finish the race and complete a successful circumnavigation."
The three who launched from London are on their way to the south coast and are taking similar routes around the world. After cycling south through Europe all three are heading for India, followed by some variation in south-east Asian countries including Thailand and Vietnam.
Then they will cross Australia, tackle a ride across New Zealand then a mammoth leg across the USA. The final leg will bring them back into Europe and north into London to the same spot they launched from today.
Mr Erande is the only rider heading west around the world and the only one taking on a significant chunk of South and Central America.
The winner of the 2012 World Cycle Race, Mike Hall, now a race ambassador, flagged off the riders and offered some advice on how to win: "It's not just about riding fast, it's about living fast, you have to ride like you're in a manhunt, and if it gets tough and you're going to cry, you cry on the bike.
"Whatever happens you have to keep moving so you stay in the race. I think this year's riders have a good chance of breaking the world record but we'll know more after a couple of weeks once they've settled into a rhythm."