India's new national census puts the population at about 1.21 billion people, or 17 per cent of the world population, the census commissioner says.

The increase of 181 million over the last decade is near what officials had estimated, C. Chandramauli said Thursday. While it is a 17.6 per cent increase from the 2001 census, population growth is slower than the previous count that showed 21.5 per cent growth.

The census indicated a continuing preference for male children over females in a country where female infanticide is still common and the government has banned hospitals from revealing the sex of unborn children to their families.

A gender breakdown among children showed fewer girls than boys are being born or surviving, with 914 girls for every 1,000 boys under the age of six, compared to 927 for every 1,000 in the last census.

"This is a matter of grave concern," Chandramauli said.

The literacy rate went up to 74 per cent nationwide for people aged seven and older, from about 65 per cent in the last census.

Officials said it would require up to a year of data analysis before official numbers could be released.