India is likely to begin conducting a long-delayed population census in September, two government sources said, as Prime Minister Narendra Modi looks to plug important data gaps in his third term after years of criticism.

India's once-a-decade census was due to be completed in 2021 but was delayed because of the COVID-19 pandemic. It will take about 18 months to complete the new survey after it begins next month, two government sources directly involved in the matter said.

Economists within the government and outside have criticised the delay in the latest census as it impacts the quality of many other statistical surveys including economic data, inflation and jobs estimates.

At present, most of these data sets - and government schemes based on their results - are based on the last population census released in 2011.

The Ministry of Home Affairs, which takes the lead in conducting the census, and the Ministry of Statistics and Programme Implementation have drawn up a timeline and are aiming to release results by March 2026, covering a period of 15 years, the officials said.

The final nod to start the process from Modi's office is awaited, one of the two officials said.

According to a United Nations report released last year, India overtook China as the world's most populous nation last year.

The home affairs and statistics ministries did not immediately respond to emailed requests for comment.

The government is also trying to overhaul its economic data including retail inflation, include a reweighting of its different categories including food to reflect changes in consumption patterns.