Governments around the world must work out how to cope with ageing, a UN report said on Monday, warning that developing nations with lots of young workers may one day find their elderly populations a burden.
The study by the United Nations Population Fund (UNFPA) and HelpAge International also urged countries to improve medical provision to extend the years of health that older people can enjoy.
The report, which was released to coincide with the International Day of Older Persons, estimates one in nine people around the world are older than 60, accounting for some 810 million of the seven billion global population.
The size of the elderly population is expected to swell by 200 million in a decade to go beyond one billion people and soar to two billion by 2050, the report said.
Alongside the report a symposium on ageing was being held in Japan -- the world's fastest-greying country -- where around a quarter of the population is over 65 already, a proportion the government forecasts will rise to 40 percent within half a century.
"The world is quickly becoming much older, and developing countries will be taking the lead in terms of speed of this process," said Babatunde Osotimehin, UNFPA executive director.
"Population ageing is one of the most significant trends in the 21st century," he told a press conference.
By 2050, the report said, some 80 percent of the world's older people will live in developing countries, many of which currently have young populations where there are many more workers than pensioners.
"In many developing countries with large populations of young people, the challenge is that governments have not put policies and practices in place to support their current older populations or made enough preparations for 2050," the two bodies said in a joint statement.
The report warned that the skills and knowledge older people possess are going to waste, with many of them under-employed and vulnerable to discrimination, abuse and violence at work and in the home.
Many of the world's elderly also live in poverty and have difficulty accessing medical care, making them vulnerable to chronic conditions such as hypertension, the bodies said.
The agencies are calling for governments and the public to end "these destructive practices and to invest in older people".
"Countries must address their ageing mismanagement, and put in place strong laws and associated plans and budgets," said Richard Blewitt, chief executive officer of HelpAge International.
He called for wider use of basic social programmes, including affordable medical care for elders, as well as the abolition of a mandatory retirement age.