India is expected to become the world's most populous nation with 1,628 million people by 2050, outpacing China with 1,437 million, a US-based research institute said on Tuesday.

China's population at present is 1,300 million while that of India is 1,087 million.

The United States' population is 294 million and is expected to touch 420 million by 2050, according to figures published by the Washington-based Population Reference Bureau.

The US is the only industrial nation whose population is increasing, half of which is attributed to immigration.

Pakistan's population, currently at 159 million, is expected to rise to 295 million by 2050, it said.

The uneven pace of population growth between developing and industrialised nations represents the world's demographic "fault line", PRB said.

Nearly 99 per cent of all population increase, it said, takes place in poor countries, while population size is static or declining in the rich nations.

As a consequence, by 2050, population in the industrialised countries is projected to increase by merely 4 per cent while that of developing countries is expected to rise by 55 per cent, PRB said.

Population in Western Europe will shrink while West Asian nations are expected to see a rise by about 186 million by 2050. Overall, world population, estimated at 6,396 million in mid-2004, is projected to increase to 9,276 million by mid-2050.