Half the world's population will live in cities in two years, a huge jump from the 30 percent residing in urban areas in 1950, UN demographers reported. Some 3.2 billion of the world's 6.5 billion people live in cities today, and the number will climb to 5 billion -- an estimated 61 percent of the global population -- by 2030, the UN Commission on Population and Development said in a report. The number of very large urban areas was also rising, the commission said. Twenty cities now have 10 million or more inhabitants, compared with just four -- Tokyo, New York-Newark, Shanghai and Mexico City -- in 1975 and just two -- New York-Newark and Tokyo -- in 1950.