With the world population reaching a milestone of seven billion on Monday, UN Secretary- General Ban Ki-moon called for international solidarity as the globe faces a multitude of crises. \"Today the world\'s population reached seven billion,\" Ban said at a press conference at the UN Headquarters in New York to mark the milestone. \"The world\'s population reached six billion in 1998, 13 years ago. It is expected to grow to 9 billion by the middle of this century, or even a few years earlier -- by 2043.\" \"This is a day about our entire human family,\" said Ban. Also on the special occasion, he drew the world attention to global scourges such as the economic and food crises. Ahead of the G20 summit in Cannes, France, Ban said his message will be \"loud and clear -- think about our children... Think about the future, with vision and foresight.\" \"Yes, we face a serious economic crisis,\" Ban said. \"For much of the world, fiscal austerity is the new order of the day. Yet even in these difficult times, we cannot afford to cut loose those who are hardest hit.\" The United Nations Population Fund (UNFPA) said in a report that the world population reached seven billion on Oct. 31, representing both challenge and opportunity for the international community. Of the world\'s seven billion, 1.8 billion are young people between the ages of 10 and 24, 60 percent are under 25 years old, the UNFPA report said.