India is projected to overtake China as the world's most populous country. (Representational)

Highlights Populations of high-income countries are expected to peak

In most of Europe, population may fall by 120 million in 2100

World population expected to reach 9.7 billion in 2050

Dynamic shifts in the world's population are underway.

In 20 years time, the populations of high-income countries are expected to peak and for many major economies population declines are already underway.

Most of Europe is shrinking and by 2100, its expected to decrease by 120 million people, from close to 750 million today to about 630 million, according to United Nations population data released today. Italy alone is expected to drop by 20 million people, Germany by nine million and the populations of Albania, Moldova, and Serbia are expected to shrink by half.

The U.K. is the main European exception. It is expected to increase its population by 10 million people. Norway, Sweden, Switzerland and Ireland are also expected to see gains.

Outside of Europe some of the population shifts are even more dramatic, India is projected to overtake China as the world's most populous country around 2027 and reach a population peak around 2060. China's population is expected to fall by 375 million by 2100.

The world population is expected to reach 9.7 billion in 2050 and could peak at nearly 11 billion around 2100.

In terms of the top 10 largest countries, Brazil, Bangladesh, Russia and Mexico are expected to be replaced by Ethiopia, Egypt, DR Congo and Tanzania. The United States drops to fourth as Nigeria takes the third spot.

"Many of the fastest growing populations are in the poorest countries," said Mr. Liu Zhenmin, United Nations Under-Secretary-General for Economic and Social Affairs.

By 2100, less than one in ten people will be Chinese from close to one in five today.