The U.N. said in a report on world trends released Tuesday that global population is expected to officially hit 6.9 billion on July 1 and 7 billion on Oct. 31. Most of the increase is expected from the world's "high-fertility countries," especially in sub-Saharan Africa.

U.N. Population Division Director Hania Zlotnik said the projections depend on expected fertility rates, with populations in many nations aging as medical advances allow people to live longer and families opt to have fewer children.

"The world hasn't collapsed by adding so many people, but most of the people have been added in the poorest countries," Zlotnik noted. "If they don't achieve the lower level of fertility we are projecting they could have serious problems."

"A world of 7 billion is both a challenge and an opportunity," said Dr. Babatunde Osotimehin, executive director of the U.N. Population Fund, which supports using population data for anti-poverty programs and policies.

"Globally, people are living longer, healthier lives and choosing to have smaller families," Osotimehim said. "But reducing inequities and finding ways to ensure the well-being of people alive today, as well as the generations that follow, will require new ways of thinking and unprecedented global cooperation."

The nongovernmental Population Action International called the projections a "wake-up call" for the international community to meet a global demand for family planning options.

"As we approach this numerical milestone, it's important to think about the individuals contained within it," said the group's president, Suzanne Ehlers. "Each one will have varying options that determine whether 7 billion becomes 9 billion or more than 11 billion by 2050."