A baby born somewhere on Tuesday will be the world's eight billionth person, according to a projection by the United Nations.

"The milestone is an occasion to celebrate diversity and advancements while considering humanity's shared responsibility for the planet," UN Secretary-General Antonio Guterres said in a statement.

The UN attributes the growth to human development, with people living longer thanks to improvements in public health, nutrition, personal hygiene and medicine.

It is also the result of higher fertility rates, particularly in the world's poorest countries – most of which are in sub-Saharan Africa.

The current population is more than three times higher than the 2.5 billion global headcount in 1950.

However, after a peak in the early 1960s, the world's population growth rate has decelerated dramatically, the UN Population Fund has said.

Annual growth has fallen from a high of 2.1 percent between 1962 and 1965 to below 1 percent in 2020.

That could potentially fall further to around 0.5 percent by 2050 due to a continued decline in fertility rates, the United Nations projects.

The UN projects the population to continue growing to about 8.5 billion in 2030, 9.7 billion in 2050, and peaking around 10.4 billion in the 2080s.

Other groups have, however, calculated different figures.

The US-based Institute for Health Metrics and Evaluation estimated in a 2020 study that the global population would max out by 2064, without ever reaching 10 billion, and decline to 8.8 billion by 2100. (AFP)