The World Health Organisation on Friday warned the world had entered a "new and dangerous phase" of the pandemic, with people tiring of lockdowns despite the disease's accelerating spread.
WHO chief Dr Tedros Adhanom Ghebreyesus urged nations and citizens to remain extremely vigilant, as the number of cases reported to the UN health agency hit a new peak.
"The pandemic is accelerating," Dr Tedros said. "More than 150,000 new cases of Covid-19 were reported to the WHO yesterday, the most in a single day so far."
He said almost half of those cases were reported from the Americas, with large numbers also being recorded in South Asia and the Middle East.
"The world is in a new and dangerous phase," Dr Tedros said. "Many people are understandably fed up with being at home.
"Countries are understandably eager to open up their societies and economies. But the virus is still spreading fast, it's still deadly and most people are still susceptible.
He said the most vulnerable people were set to suffer the worst.
It emerged that the virus was present in Italy in December, months before its first confirmed cases and about the same time as the disease was first reported in China.
The virus, which has now killed more than 468,000 people and infected at least 8.9 million people worldwide, is surging in the Americas and parts of Asia, as Europe starts to ease restrictive measures.
A vaccine remains months off at best despite several trials, while scientists are still discovering more about the virus, its symptoms and the extent to which it may have spread before being identified.
Italian researchers discovered genetic traces in samples of waste water collected in Milan and Turin at the end of last year, and Bologna in January, the ISS institute said.
Italy's first confirmed cases were not until February.
The results "help to understand the start of the circulation of the virus in Italy", the ISS said.
Italy was the first European country to be hit by the virus and in early March became the first to impose a nationwide lockdown.
In a sign of the persisting risks, Italy's top health agency ISS also urged caution after last week seeing "warning signs" of virus transmission following two outbreaks in Rome.
"In certain parts of the country, the circulation of the virus is still significant," the ISS said in its weekly report.
Many European countries followed Italy into lockdown and most have only begun reopening this month after painful shutdowns that devastated their economies.
Facing the biggest recession in the EU's history, leaders on Friday held a virtual summit on the European Commission's proposal for a €750 billion (Dh3.08 trillion/$838.73bn) rescue fund.
But they fell short of reaching a deal on a plan regarded as a key gesture of the bloc's solidarity and unity.
Opposition is fierce from the "frugal four", comprising the Netherlands, Sweden, Denmark and Austria.
But Italy and Spain, the first and hardest hit by the pandemic, were already crippled by overstretched finances.
Chinese scientists have said the virus probably emerged in a market that sold wildlife in the central city of Wuhan in December, but Beijing officials have recently suggested it may have originated elsewhere.
After largely bringing the virus under control and easing restrictions, China is now fighting a resurgence after finding a cluster centred on a market in Beijing.
Authorities launched a nationwide campaign to inspect food imports, while tens of thousands of people are also being tested and neighbourhoods have been locked down.
Chinese authorities said studies of genome data, which it shared with the WHO, suggest the new outbreak in Beijing "came from Europe", but is different from what is spreading there.
"It is older than the virus currently circulating in Europe," said Zhang Yong of the Chinese Centre for Disease Control and Prevention.
Mr Zhang raised the possibility of the virus lurking in imported frozen food or the wholesale market, resulting in similarities to older strains.
The US still leads the world in the number of confirmed infections and deaths, with a recent surge in southern states.
The economy has also been hammered in a year when US President Donald Trump seeks re-election.
But top US expert Dr Anthony Fauci offered hope as he said that he did not see America returning to another lockdown.
Dr Fauci predicted it would focus on "trying to better control those areas of the country that seem to be having a surge of cases".
He was optimistic the world would soon have a vaccine to end the pandemic, telling AFP that early trial results were "encouraging".
But Apple said it was closing some shops in US states that were experiencing a surge in infections, reversing course after reopening many of its locations.
The Philadelphia Phillies baseball team said five players and three staff tested positive for Covid-19 at the club's Clearwater training base in Florida.
But normality is returning to cultural and sporting events disrupted by the virus.
Football returned to hard-hit South America on Thursday after a three-month hiatus, with a Rio state tournament match in Brazil.
