India reached the grim milestone of 400,000 deaths from Covid-19 on Friday, half of them during a second wave of the coronavirus pandemic in the past few months that overwhelmed the healthcare system and crematoriums. India has recorded 30.45 million cases since the outbreak of the pandemic last year, and is the second most affected country behind the United States, which has 33 million cases. The US has reported more than 604,000 deaths while in Brazil, about 518,000 people have died. India, the world's second most populous nation, recorded 853 deaths in the past 24 hours, health ministry data showed on Friday. That took it past the 400,000 mark, with the last 100,000 being added in just 39 days, according to a Reuters tally. But health experts believe India may have undercounted deaths significantly and that the actual number could be one million or even higher. Scores of bodies washed up along the Ganges river in northern India in May, as people struggled to keep pace with deaths and cremations at the peak of the second wave. “Undercounting of deaths is something that has happened across states, mostly because of lags in the system, so that means we will never have a true idea of how many people we lost in this second wave,” said Rijo M John, a professor at the Rajagiri College of Social Sciences in the southern city of Kochi. Last month Bihar, one of India's poorest states, revised its Covid-19 death toll to 9,429 from 5,424, after an order from a local court. India had recorded 200,000 deaths at the end of April, but took just 28 days to get to 300,000 deaths. Hospitals ran out of beds and life-saving oxygen during the second wave in April and May and people died while waiting for treatment outside hospitals and at their homes. Case numbers have declined steadily since hitting a peak in May, but government officials and experts said that a third wave is imminent as the country slowly reopens and a new variant of the virus, locally called the Delta Plus, rears its head.