Spreading slums, violence and rising poverty are among the challenges facing cities as the world's urban population swells to an estimated 5 billion people by 2030, a report from the U.N.'s housing agency says. The "State of the World's Cities" report attacked the argument that unfettered trade is a sure route to wider developing-world prosperity and warned of a "race to the bottom" as companies seeking cheaper labour shift capital and jobs across borders. The U.N.-Habitat agency, due to present the report at a major international conference in Barcelona on Tuesday, said its aim was to investigate the impact of globalisation on cities already altered by massive waves of international migration. "Many cities face ... growing poverty, deepening inequality and polarisation, widespread corruption at the local level, high rates of urban crime and violence," U.N. Secretary General Kofi Annan wrote in a foreword to the report. City dwellers are expected to make up 60 percent of the world's population by 2030 compared with 47.7 percent in 2001 when some 2.9 billion people lived in cities. Nearly all of this increase -- equivalent to the population of a mid-sized city like Hanoi or Pittsburgh each week -- will be in the world's least developed regions, and by 2030 almost 2 billion people will live in slums. --More 2334 Local Time 2034 GMT