The UN agency said globally the births of nearly 230 million children under five have never been recorded, with Asia being the home to more than half of these children (59 per cent).
Another 37 per cent live in sub-Saharan Africa and the remaining four per cent are from other regions.
In 2012 alone, 57 million infants, four out of every ten babies delivered worldwide that year, were not registered with civil authorities.
"Birth registration is more than just a right. It is how societies first recognise and acknowledge a child's identity and existence," Geeta Rao Gupta, UNICEF Deputy Executive Director, said at a news conference here yesterday.
"Birth registration is also key to guaranteeing that children are not forgotten, denied their rights or hidden from the progress of their nations," Gupta said.
The new report, 'Every Child's Birth Right: Inequities and trends in birth registration', collects statistical analysis spanning 161 countries and presents the latest available country data and estimates on birth registration.
Among the 10 countries with the largest numbers of unregistered children, India has 71 million, the most, followed by Nigeria at 17 million.
"Nearly one in three unregistered children live in India," UNICEF said, adding that the lowest levels of birth registration in India are found among children from the two largest population groups – Hindus and Muslims.
Children from religious minorities, such as the Sikhs and Jains, are about twice as likely to be registered.
The 10 countries with the lowest birth registration levels are: Somalia (3 per cent), Liberia (4 per cent), Ethiopia (7 per cent), Zambia (14 per cent), Chad (16 per cent), Tanzania (16 per cent), Yemen (17 per cent), Guinea-Bissau (24 per cent), Pakistan (27 per cent) and Democratic Republic of the Congo (28 per cent).
Gupta said while India's birth registration level was 41 per cent nationwide, there was a huge gap between states with the highest rates and those with the lowest, due mainly to accessibility and infrastructure issues.