China will grow from 1.3 billion people today to more than 1.4 billion in 2050, an 11% increase, the Washington-based Population Reference Bureau (PRB) said on Tuesday.
India currently has nearly 1.1 billion people.
The population of Japan, the world's second richest country, will shrink by 21%, from 127.6 million people to 100.6 million.
Two war-ravaged nations will experience a massive population boom.
Afghanistan's population will nearly triple, from 28.5 million to 81.9 million, while Iraq's will more than double, from 25.9 million people today to 57.9 million in 2050.
Huge increases in population are
predicted for many Asian nations
Asia will continue being the world's most populous continent as its population will rise to nearly 5.4 billion people by 2050, a 39% growth, the PRB said.
The world population will grow at an even quicker pace, from 6.4 billion people today to about 9.3 billion in 2050, a 45% increase.
In other parts of Asia, Pakistan's population will jump by 85%, from 159.2 million people today to 295 million in 2050.
Indonesia will remain the fourth most populous nation in the world, after the United States. Its population will grow by 41%, from 218.7 million to 308.5 million.