Hundreds of people, the majority of them young people responding to a message from Flash Mob DF, rode the Mexico City Metro over the weekend in their underwear as part of a project by social-networking sites to get strangers to meet.

The mass event, which ended with a huge group photo Sunday around the Monument to the Revolution, was marked by a festive air from start to finish.

Many of the partially clothed riders gathered at the monument while others met at the Refineria station next to Parque Bicentenario to start their trips.

Metro employees acted respectfully toward the riders, who drew curious looks from some fellow riders, while other people appeared oblivious to what was going on.

Some of the young people wore wrestling masks, Mexican sombreros or painted their faces, and all of them appeared to be having a good time.

Participants posted photos and comments about the event on Twitter (#NoPantsMX).

The Mexico City Metro carries about 4 million people each day, but ridership tends to be much lower on Sundays. EFE