The official global death toll for 2020 was 1.8m people, but presenting its annual World Health Statistics report, the WHO estimated that total deaths from the COVID-19 pandemic in 2020 were at least 3m.
"We are likely facing a significant undercount of total deaths directly and indirectly attributed to COVID-19," it said.
WHO data analyst William Msemburi said this estimate included both unreported COVID-19 deaths – where people did not get tested – as well as indirect deaths due to the lack of hospital capacity and other restrictions.
"Excess mortality gives us a better picture, because it captures both of these direct and indirect effects," Msemburi said.
The UN agency officially estimates that around 3.4m people have died directly as a result of the COVID-19 pandemic by May 2021. But the overall excess mortality figures suggest the true count is higher.
"This number would truly be two to three times higher. So I think safely about 6m to 8m deaths could be an estimate on a cautionary note," said Samira Asma, WHO's assistant director-general in its data and analytics division at a virtual press briefing.
Every country is facing challenges to report COVID-19 deaths and WHO said it was working with countries "to understand the true human toll of the pandemic so we can be better prepared for the next emergency."