Asia is home to the planet's two most populous countries - China and India - and more than half the world's six and a half billion people.

And statistics show the Asian population is aging - presenting challenges on how a smaller, younger generation will care for a much larger, older generation.

The United Nations projects the number of Asians aged 65 and older will increase more than 300 percent between the years 2000 and 2050 - from 207 million to 857 million.

Population expert Andrew Mason, at the University of Hawaii, says how governments prepare now will directly affect the quality of life for young and old in a few decades. 

"We consistently underestimate the pace of aging. I think the changes in age structure will be greater, aging will be faster that what people anticipate, and so we better develop ways to deal with it, and we'd better hurry," Mason says.

Japan, South Korea, and Singapore are already dealing with a larger proportion of elderly in relation to the 15-to-64 year-old working-age group. 

But most Asian countries will experience the shift in age structure in 15 to 20 years.

The U.N. Population Fund is working with regional governments to begin preparing now.  One of the main challenges is poverty.  Many Asian nations are simply too poor to fund large-scale public pensions and health care programs.

Garimella Giridhar is an Asia expert with the U.N. Population Fund in Bangkok.

"In these countries that I am talking about - in Indonesia, in Vietnam - the government services are quite inadequate. And if people begin to depend on those non-existing services, that will be a major problem," Giridhar says.

Some governments in less developed countries are, instead, looking to build on the Asian tradition of families caring for elderly parents. For example, Malaysia gives priority housing to adults who have parents living with them. Both the Philippines and Malaysia offer tax breaks for relatives caring for elderly family members.

But the tradition is not enduring in all parts of Asia. Ideas about familial obligations seem to be changing with rising affluence. Hong Kong resident Albert Leung says he plans to have enough savings when he retires and he does not expect his children to support him.

"For our case, I always say we won't be relying on them. People in Hong Kong [are] still on a more traditional Chinese way of thinking that they hope their children will care for them," Leung says. "But I suppose this is changing now."

The challenges that come with the graying of Asia are, in many cases, a direct result of successful programs in recent decades to reduce the population. In major countries in Asia, the birth rate has been going down for the last 50 years. Between 1960 and 1990, Thailand and China dramatically reduced their birth rates from an average of more than four children per woman to around two.

That means there are less young people to enter the work force and pay taxes to support retirees.

So the U.N. Population Fund says the focus is shifting from traditional welfare-type pension programs to helping older people remain vital longer.

Demographer Mason, of the University of Hawaii, says one way to do this is to raise the retirement age.

"Retirement is also surprisingly young, so 58, 59, 60 seem to be the ages at which people seem to be withdrawing from the labor force, and earning less than they are consuming," Mason added.

Another issue is how to make sure the older generation is not only allowed to work longer, but is attractive to employers. Malaysia provides job retraining and job placement. The Philippines and Singapore offer employers of older people incentives in the form of tax deductions.

Experts seem to agree that finding creative solutions is key to balancing population changes and needs.

The task is so immense, the U.N. says, that the responsibility of caring for the elderly must be shared among individuals, families, communities, non-governmental organizations, and governments.