Beijing:
The world is expected to reach a population milestone at the end of October. According to the UN Population Fund, there will be seven billion people sharing the planet's land and resources.
In Western Europe, Japan and Russia, it comes amid worries about low birth rates and ageing populations.
In China and India, the two most populous nations in the world, it is an occasion to reassess policies that have already slowed once-rapid growth.
China is home to 1.34 (b) billion people, but the number of babies being born is now on the decline.
According to US Census projections, the population should begin to shrink in 2027. By 2050, it will be smaller that it is today.
The pace of the growth has slowed due to a one child policy and also a rise in the cost of living.
The one child policy was introduced in 1979 and, according to Chinese authorities, it has prevented around 400 (m) million births between 1979 and 2011.
In the 1970s, Chinese women had an average of five or six children. Duan Yanling, a 28-year-old only child from northern China, moved to Beijing with her parents. She is now married, works as an English teacher, and has a two year old son.
As she and her husband are both single children, they qualify for having a second baby. But economic pressures have become a deciding factor.
"The fewer children you raise, the less money you pay. In today's society, people have a lot of work pressure. So it improves your life if you give birth to fewer children," Duan Yanling said.
Three decades of strict family planning rules have also pushed many parents who want a son to resort to selective abortions, which is reflected in the skewed population sex ratio.
China's population growth is bringing many challenges, including an aging population, with a lack of social security, proper medical care and pension provision.
The current population growth has produced an over-supply of labour, especially in rural areas, so that many still flock to the cities to find work, often facing poor conditions and low wages.
At the Development Centre for Rural Women, trainees migrating to the cities receive basic technical assistance to help them secure work.
17-year-old Chen Zengzeng from Henan, one of China's poorest provinces, is training to be a typist.
"If you don't master a skill of your own, finding a job will be very hard," she said.
Wu Qing, a retired professor and former delegate for her district to the National People's Congress, set up the training centre.
According to Wu, Chinese migrants are seeking better living standards.
She wants the government to allow people to move easily within the country without needing a permit.
Meanwhile, in India, already the second most populous country, with 1.2 (b) billion people, the country is expected to overtake China around 2030 when its population soars to an estimated 1.6 (b) billion.
But even as the numbers increase, the pace of the growth has slowed.
Demographers say India's fertility rate - now 2.6 children per woman - should fall to 2.1 by 2025 and to 1.8 by 2035.
More than half of India's population is under 25, and some policy planners say this so-called "youth dividend" could fuel a productive surge over the next few decades.
"As the fertility has been falling, what has happened is that the population in the productive ages has increased, it will be much higher than before and, as a result, we are in this process of demographic dividend," said demographer Shereen Jejeebhoy.
But population experts caution that the dividend could prove a liability without vast social investments.
"I think we are too obsessed on the numbers. We need to start thinking how can we best enable our population to be healthy, educated, skilled and ready to make a contribution to the future of our country,"
Jejeebhoy added.
Population experts also worry about a growing gender gap, stemming largely from Indian families' preference for sons.
A surge in sex-selection tests, resulting in abortion of female foetuses, has skewed the ratio, with the latest census showing 914 girls under age 6 for every 1,000 boys.
Family planning is a sensitive issue.
In the 35 years since one government was toppled for pursuing an aggressive population control programme, subsequent leaders have been reluctant to follow suit.
So with the seven (b) billion population milestone approaching, is the world facing a catastrophe? Not necessarily.
But experts say most of Africa and other high-growth developing nations such as Afghanistan and Pakistan will be hard-pressed to furnish enough food, water and jobs for their people, especially without major new family-planning initiatives.
According to Lester Brown, who heads the Earth Policy Institute in Washington, DC, extreme poverty and large families tend to reinforce each other.
The challenge, he says, is to intervene in that cycle and accelerate the shift to smaller families.
"There are roughly 215 million women in the world today who want to plan their families but can't afford the family planning services or don't have access to them for some reason," Brown said.
"If we fill that family planning gap, we would almost stabilise world population, not quite. But these 215) million women and their families total well over one billion and they are essentially the poorest billion people in the world."
Brown added that without the means to plan smaller families, numbers will inevitably keep growing.
"There will be 219,000 people at the dinner table tonight who were not there last night and tomorrow night there will be another 219,000 people at the dinner table," he said.
"This has been going on for decades now and, at some point, adding this many people every day, having to produce this much more food every day begins to stress the earth's land and water resources and that's what we are seeing now."
Looking ahead, the UN projects that the world population will reach 8 (b) billion by 2025, and 10 (b) billion by 2083.
But the numbers could be much higher or lower, depending on such factors as access to birth control, infant mortality rates and average life expectancy, which has risen from 48 years in 1950 to 69 years today.