India registered about 475,000 more total deaths in 2020 than the previous year, government data released months ahead of schedule on Tuesday showed, as the World Health Organisation (WHO) readies its estimates of excess Covid-19 deaths whose methodology New Delhi has opposed.

Some experts estimate India's actual Covid death toll is as high as 4 million, about eight times the official figure, especially as a record wave driven by the Delta variant killed many people in April and May of last year. The WHO's estimate will be published on Thursday.

Vinod Kumar Paul, a top health official who has overseen India's fight against the pandemic, said there was nothing "dramatic" in the total death data for 2020 and that those were "absolute, correct and counted numbers".

He said the data showing 8.1 million total deaths in India in 2020 was released by the Office of the Registrar General two to three months in advance because of the attention on the country's Covid toll.

"There is a public narrative in the media, based on various modelling estimates, that India's Covid-19 deaths are many times the reported figure - that's not the case in reality," he told state TV.

"We now have actual data for 2020, there is no need to do any modelling now. We will have actual, robust data for 2021 too. Modelling can lead to overestimation, absurd estimation."

The death count grew slower in the country of 1.35 billion people in 2020 than in the previous two years, the data showed.

India officially reported 148,738 Covid-19 deaths in 2020, with the tally jumping to 523,889 on Tuesday out of more than 43 million cumulative infections. Only the United States and Brazil have recorded more deaths as of Tuesday.

Countries around the world reported only 1.83 million Covid-19 deaths in 2020 but the WHO estimates excess mortality of at least 3 million globally for that year.

India has said it does not agree with the WHO's methodology, though the scientists working on the latest estimates have defended it.