The world's seven billionth person will be born today in what UN leader Ban Ki-moon calls a "world of contradiction" -- and facing an uphill battle if it is on the wrong side of the poverty line.

While many countries around the world will be choosing their own symbolic baby, holding rallies and other events to mark the latest stage of the global population explosion, Ban will not be seen cuddling a newborn.

According to the UN secretary general, the seven billion day is no laughing matter.

Ban said he suspects the seven billionth person, wherever he or she is born, "will be born into a world of contradiction."

"Plenty of food, but still a billion people going to bed hungry every night. Many people enjoy luxurious lifestyles, but still many people are impoverished," he said in an interview with Time magazine.

Monday's birth should be seen as a "clarion call to action," he insisted.

An extra billion people have been added to the world's population since just after midnight on October 12, 1999 when the United Nations named a Bosnian baby, Adnan Mevic, as the Earth's six billionth inhabitant.

The secretary general at the time, Kofi Annan, was pictured in a Sarajevo hospital with Mevic in his arms.

The Mevic family is now struggling in poverty at their Sarajevo home, which is partly why no baby will be put in the global spotlight this time.

"This is not a story about numbers. This is a story about people," Ban said at a New York school last week.

"Seven billion people who need enough food. Enough energy. Good opportunities in life for jobs and education. Rights and freedoms. The freedom to speak. The freedom to raise their own children in peace and security.

"Everything you want for yourself -- seven billion times over," he told students.

The UN chief will be taking his message to the Group of 20 summit in France this week. A growing population and global economic crisis means leaders need to brace for more protests like the Arab Spring and Occupy Wall Street in the United States.

"The gathering force of public protest is the popular expression of an obvious fact: that growing economic uncertainty, market volatility and mounting inequality have reached a point of crisis," he said in a letter to G20 leaders ahead of the November 3-4 summit.

Plenty of food, but still a billion people going to bed hungry every night. Many people enjoy luxurious lifestyles, but still many people are impoverished- UN Secretary General

With about two babies being born every second, the seven billion figure will keep racing ahead in decades to come -- to more than 10 billion by 2100, according to UN estimates.

The UN predicts that India will overtake China as the world's most populous nation by 2025, when it will have almost 1.5 billion people. Experts say the whole world will face huge challenges containing poverty and saving the environment.

A new UN Population Fund (UNFPA) report highlights how the world will face growing problems finding jobs for the new army of young people, especially in poor countries; how climate change and population growth are adding to drought and famine crises; and managing urban sprawl as Tokyo's agglomeration hits a population of 36.7 million people.

Japan and many European countries are worrying about their ageing populations -- a situation which has implications for migration, health and labour planning.

UNFPA executive director Babatunde Osotimehin is also among those calling for less focus on the big numbers.

"This is not a matter of space -- it's a matter of equity, opportunity and social justice," he said.

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