Bulgaria is expected to have the world's highest population decline rate between 2015 and 2050, a UN report shows.

The Southeastern European country is among the 48 whose population is expected to shrink over the next 35 years. It is part of the group where a decrease of more than 15% is expected between 2015-2050, alongside Bosnia-Herzegovina, Croatia, Hungary, Japan, Latvia, Lithuania, Moldova, Romania, Serbia and Ukraine.

Bulgaria has a population of roughly 7.15 million as of 2015, a number that is projected to go down to 5.154 m in 35 years, the UN says.

This suggest a decrease of 27.9%, the biggest in the world according to a table that is part of the UN report's key findings.

Romania comes second with 22.1%, and the first ten positions are entirely dominated by Eastern European countries.

By 2100, the Bulgaria's population is expected to have decreased to 3.4 million.

In a table representing a list of ten countries with the oldest and the youngest populations for 1950, 1980, 2015, 2030, and 2050, Bulgaria ranks 7th as of the current year, but is not present elsewhere in the "top 10" list.

Fertility in European countries in general "is now below the level required for full replacement of the population in the long run (around 2.1 children per woman, on average), and in the majority of cases, fertility has been below the replacement level for several decades."

"Fertility for Europe as a whole is projected to increase from 1.6 children per women in 2010-2015 to 1.8 in 2045-2050, but such an increase will not prevent a likely contraction of the total
population size," the report has added.

The 2015 Revision of World Population Prospects also shows that India will become the world's most populous country in just seven years, when it will be home to more people than China. India and China's population are currently 1.31 b and 1.38 b, respectively, but both will have about 1.4 people by 2022, and after 2030 China's population will see a slight decrease, the international body estimates.

The world's overall population is projected to grow to 9.7 billion by 2050 and to 11.2 billion by 2100, with more than 9 billion people living in Africa and Asia at the end of the century.