Sky News reports that some 39,897 people crowded into the Mexican capital for the attempt, beating the previous record when 32,648 people puckered up in Weston-super-Mare on 2007.
"There are 42,225 people on site, but unfortunately you did not all participate in the record," said Carlos Martinez, who verified the event for Guinness World Records.
The giant Zocalo, which can hold 100,000 people, was half-filled as mostly young couples embraced and held one another in a lip lock for 10 seconds.
As the crowds gathered, workers in cupid wings offered hugs, teenage boys carried signs volunteering their kissing services, and couples practised openly in the streets.
Benito Zavala, 53, who works in a nearby store, said he did not have time to go home to get his wife. So he planned to help set the record with his two-year-old Chihuahua, Onix.
Tourist chiefs organised the kiss-off in protest at the soaring drug violence in the country, which claimed more than 6,000 lives last year.
Organisers said that it also aimed to send a message to a local mayor who tried to ban kissing in the public square.
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