Two people are dead and 11 are missing after an explosion that caused at least one 18-story building to collapse in downtown Rio de Janeiro on Wednesday. Brazil’s Globo News is reporting that as many as three buildings may have collapsed after what witnesses described as a sudden violent explosion. Though the cause of the blast is not yet known, first responders met a strong smell of gas and a fire started by the collapse. The AFP reported that 30 people were rescued from buildings close by. The city's mayor, however, says that there probably wasn't an explosion, and that the building collapsed because of structural issues. Recently, there have been concerns about Rio de Janiero's shaky infrastructure, as Brazil is set to host the World Cup in 2014--and the Olympics two years later.