The world's population will increase by 40 per cent to 9.1 billion in 2050, according to the United Nations.
The report published yesterday by the United Nations Population Division said almost all this growth will come the developing world, with the population in less developed countries expected to grow from 5.3 billion today to 7.8 billion in 2050.
By contrast, the population of richer developed countries will remain mostly unchanged, at 1.2 billion.
"It is going to be a strain on the world," said Ms Hania Zlotnik, the division's new director. She said the expected growth will be concentrated in countries that already struggle to provide adequate shelter, health care and education.
The report reconfirmed many trends, including an increasingly ageing population in developed countries. But it said immigration would prevent the overall population in richer countries from declining.
The United States is projected to be the major net recipient of international migrants, 1.1 million annually, with its population increasing from 298 million in 2005 to 394 million in 2050, the report said.
Between 2005 and 2050, population growth in eight countries - India, Pakistan, Nigeria, Congo, Bangladesh, Uganda, the United States, Ethiopia and China - is likely to make up half the world's increase, the report said.
AP