(MSNBC) - Tens of thousands of revelers showered each other with sparkling wine and waved red kerchiefs Friday as the blast of a small rocket signaled the start of this year's running of the bulls. Spain's most famous summer festival kicked off in the jam-packed and cobblestoned main square of the northern town of Pamplona. People from around the world, many wearing the traditional red kerchief and white shirt and pants, roared their approval as an official on a city hall balcony declared the San Fermin festival under way. He then lit the rocket, its boom echoing through the plaza.