Visitors on the observation deck of the world's tallest tower heard a loud boom, then saw dust that looked like smoke seeping through a crack in an elevator door 124 floors above the ground.

Dubai opened the world's tallest skyscraper Monday in a blaze of fireworks, then added a final flourish: It renamed the half-mile-high tower in honor of the president of the UAE.

The Burj Dubai tower is pictured during the opening ceremony of the Burj Dubai tower on January 4, 2010 in Dubai, United Arab Emirates.The Burj Dubai is, at 824.55 meters, ...