A census of India's estimated 1.2 billion people is to begin Thursday, the IANS news agency reported.
Home Secretary G K Pillai said 2.5 million people would be involved in taking the census, India's 15th since 1872, DPA reported.
The census is to cover the country's 35 states and union territories.
Pillai said data would be collected on a range of questions including economic activity, language, education, fertility, caste and religion.
Information on the ownership of mobile phones and computers, access to the internet and drinking water quality is to be collected for the first time. Fingerprints and photos will also be taken.
The government said it plans to create a National Population Register, a database that would allow a biometrics-based identity system and the issuing of identity cards to all Indians.
Pillai said the census would be carried out in two phases.
The house listing and housing census is due to be carried out between this month and July, followed by the population enumeration phase to be done simultaneously in all areas of the country in February next year.
Retired state and central government employees are to be hired to help out in the mammoth exercise because of a shortage of officials, the PTI news agency reported.
Some 695 ex-employees are to be rehired on extendable six-month contracts.
India's census of 1.2 billion people begins
A census of India's estimated 1.2 billion people is to begin Thursday, the IANS news agency reported.