UN chief Antonio Guterres lamented the “painful new threshold” of 5 million lives “cut short by a merciless virus that respects no borders” and said vaccines were still being hogged by rich nations.
“This devastating milestone reminds us that we are failing much of the world,” the secretary general said.
“While wealthy countries are rolling-out third doses of the Covid-19 vaccine, only about five per cent of people in Africa are fully vaccinated.”
His comments came as Johns Hopkins University in Baltimore confirmed reports of 5 million Covid-19 deaths since the outbreak emerged in China in December 2019.
The WHO says the pandemic's overall toll could be two to three times higher than official records, due to deaths directly and indirectly linked to Covid-19.
More than 246,317,000 cases of coronavirus have been registered globally. The vast majority of those infected have recovered, though some experience symptoms weeks or even months later.
Many less severe or symptom-free Covid-19 cases go undetected.
Death tolls continue to climb around the world
On Saturday, 6,238 new deaths and 399,027 new cases were recorded worldwide. The countries with the highest number of new deaths were Russia (1,158), followed by India (446) and Romania (413).
Overall, the US is the worst-affected country globally with more than 745,000 deaths from some 45,954,000 cases. Other hard-hit nations include Brazil, India, Mexico and Russia.
Peru is the worst-hit country, relative to population size, with 200,000 deaths from a population of less than 33 million.
China was on Sunday working hard to contain fresh Covid-19 surges. State news outlet CCTV said thousands of tourists visiting China's Inner Mongolia region had been sent to hotels to spend two weeks in quarantine amid an outbreak there.
Slovenia’s Health Minister Janez Poklukar this week warned that a surge in infections could prompt a lockdown in the small central European nation – raising fears in other low-vaccination countries across central and eastern Europe.
The five million deaths milestone was passed after US President Joe Biden met other world leaders in Rome for a G20 summit. He was then due to travel to Glasgow, Scotland, for the UN's Cop26 climate change gathering.
Mr Biden and other leaders are looking at how to turn the page on the pandemic and focus on the deepening threat from climate change.
Still, vaccine sceptics were among the protesters on the streets of the Italian capital, and vaccine mandates have resulted in blowback against the Biden administration and other governments that seek to impose them.
Mr Guterres urged leaders to follow the UN’s global vaccine plan and get 40 per cent of humanity inoculated this year, and 70 per cent of the world population by the end of 2022.
“It would be a mistake to think that the pandemic is over,” said Mr Guterres.
“As restrictions ease in many places, we must also match vaccines with vigilance – including through smart and proven public health measures like masking and social distancing.”