The families of the four missing British sailors urged rescuers to "bring our loved ones home" as the search to find them resumed.
The four men - experienced captain Andrew Bridge, 22, and crew members James Male, 23, Steve Warren, 52, and Paul Goslin, 56 - have been missing since their yacht capsized in the Atlantic Ocean on Friday.
The US Coast Guard, who called off the search on Sunday, have now had a change of heart .
The men's families travelled to London and said they had a "very positive" meeting with foreign minster Hugh Robertson.
Speaking on the steps of the Foreign Office in Whitehall, J ames Male's father Graham Male said: "We have just had a very positive meeting and can confirm the search is continuing with immediate effect.
"We would like to thank the UK, the US and Canadian governments and coastguards for making this possible. We would sincerely like to thank the public, the celebrities, the yachting community and the merchant vessels without whom we would never have got this far.
"Please do continue to show your support by continuing to sign the online petitions. Now let's bring our loved ones home."
The families then went to the US Embassy in London to meet the homeland attache.
Cressida Goslin, wife of Paul Goslin, said they had been set to call on Prime Minister David Cameron to apply pressure on US president Barack Obama after the Coast Guard called off their search, but now do not need to.
She said: "It's been a complete emotional rollercoaster. We've had discussions with the Foreign Office in the night even though the US wouldn't budge and then we thought they would, and then they wouldn't.
"We're just really pleased.
"Hopes are still high, they've got much higher in the last hour.
"It's worked. And all the media attention has really helped and we're so grateful to everyone."
Ms Goslin said that "you can't argue with" the fact that two days had been lost, but accepted that the weather conditions would not have helped.
"It would have been difficult for air support to have the visibility to do anything anyway so if we've only got a limited amount of searching we need it when it's good visibility," she said.
The crew of the 40ft Cheeki Rafiki ran into difficulties about 620 miles east of Cape Cod in Massachusetts last Thursday while returning to the UK from a regatta in Antigua. Contact with the yacht was lost in the early hours of Friday when they diverted to the Azores.
The Coast Guard, Canadian aircraft and three merchant vessels searched for them throughout Friday and Saturday but called off efforts on Sunday at 5am local time amid treacherous weather.
Prime Minister David Cameron said: "My thanks to the US Coast Guard, which has resumed its search for our missing yachtsmen."
Mr Bridge's grandmother Valerie said: "We are delighted. It might not come to anything but people want them to do it and they are trying. It seemed too quick, just two days and we were saying 'if only they could do it (search) for a bit longer'. You never know what could happen."
By 3.30pm today more than 197,200 had signed an online petition supporting the campaign to resume the search. Nicola Evans, Mr Bridge's friend who started the petition, said the missing men have now been given a "fighting chance".
Health Secretary Jeremy Hunt, the local MP for one of the missing men, had appealed to the US Coast Guard not to give up, while entrepreneur and adventurer Sir Richard Branson urged vessels near the area to keep a lookout.
Some 4,000 square miles were scanned for the vessel's two personal location GPS beacons until no more transmissions were received from the small devices, which have a short battery life.
On Saturday, a cargo vessel which was helping with the search spotted and photographed an overturned hull which matched the description of the Cheeki Rafiki but reported no signs of people on board or a life raft.
Dame Ellen MacArthur, who twice broke the world record for fastest solo circumnavigation of the globe, said there was "every chance" that the sailors were still alive either inside the hull or in the life raft.
Mike Golding, one of the few yachtsmen to have sailed around the world non-stop in both directions, said: "From the images, the yacht has lost the keel, initially they were sinking, taking on water.
"One imagines they put out the mayday, prepared themselves for sinking, then the keel fell off, maybe the boat rolled over fast and the question is: what happened at that point? Were they able to launch the life raft at that point?"
Four-time Olympic sailing champion Sir Ben Ainslie told BBC News: "If there is a chance they are still out there, then we need to keep looking for them, so it is fantastic news that the US Coast Guard have agreed to get back out there. They should be commended for that."
Sir Robin Knox-Johnston, the first man to sail non-stop round the world, said: "The US Coast Guard and US Navy are the best at this, they have the most experience and they have the assets."
Efforts should be focused towards "just one more sweep downwind of where the hull was discovered", he suggested "so that people can feel that everything that could be done has been done".
In the meeting Mr Robertson assured the families that the G overnment has been in constant contact with the US and it " will do everything possible to try and locate these missing yachtsmen."
The US Coast Guard said that several aircraft and vessels are now trying to find the yachtsmen.
Crews from the US Coast Guard, US Air Force, Canadian military are now "en route".
From the air, the operation includes the HC-130 Hercules aircraft from the US Coast Guard Air Station Elizabeth City, North Carolina, the US Coast Guard Cutter Vigorous, from Cape May, New Jersey, and a US Air Force C-130 aircraft from Moody Air Force Base, in Valdosta, Georgia. The Canadian military C-130 aircraft is part of the operation.
A 672-ft motor vessel Premium Do Brasil, with the 751-ft motor vessel AM Hamburg, the 600-ft motor vessel Bow Flora, the 477-ft motor vessel Chem Venus, and the 551-ft motor vessel Independent Accord have also been pressed in to action.
In a statement the US Coast Guard also noted: "The 1st Coast Guard District covers from New Jersey to Canada with search and rescue duties extending approximately 1,300 miles from shore. Units across the Northeast conduct more than 2,500 search and rescue cases in a year, and rescue more than 300 people."
In its statement the US Coast Guard recalled that an overturned hull that matched the description of the Cheeki Rafiki was seen but no sign of the sailors on Saturday at approximately 12pm.
It added: "Rescue crews located small debris fields, indicating that search patterns were accurate, but there were no signs of life or a life raft.
"The active search was suspended at 5am, Sunday after two days of searching with no indication of surviving crew members."