More than 136,000 cases were reported worldwide on Sunday, "the most in a single day so far", WHO Director General Tedros Adhanom Ghebreyesus said.
"More than six months into the pandemic, this is not the time for any country to take its foot off the pedal," he told an online briefing on Monday.
In response to a question on China, WHO's top emergencies expert, Dr Mike Ryan, said retrospective studies of how the outbreak has been addressed could wait, adding: "We need to focus now on what we are doing today to prevent second peaks."
Ryan also said infections in central American countries including Guatemala were still on the rise, and that they were "complex" epidemics.
"I think this is a time of great concern," he said, calling for strong government leadership and international support for the region.
Brazil is now one of the hotspots of the pandemic, with the second highest number of confirmed cases, behind only the United States, and a death toll that last week surpassed Italy's.
After removing cumulative numbers for coronavirus deaths in Brazil from a national website, the Health Ministry sowed further confusion and controversy by releasing two contradictory sets of figures for the latest tally of infection cases and fatalities.
Ryan said Brazil's data had been "extremely detailed" so far but stressed it was important for Brazilians to understand where the virus is and how to manage risk, and that the WHO hoped communication would be "consistent and transparent".
Maria van Kerkhove, a WHO epidemiologist, said that a "comprehensive approach" was essential in South America.
More than 7 million people have been reported infected with the coronavirus globally and over 400,000 have died.
"This is far from over," van Kerkhove said.
At least half of Singapore's newly discovered coronavirus cases show no symptoms, the co-head of the government's virus taskforce told Reuters on Monday, reinforcing the city-state's decision to ease lockdown restrictions very gradually.
Van Kerkhove said that many countries doing contact tracing had identified asymptomatic cases but were not finding that they caused further spread of the virus, adding: "It is very rare".
Ryan, asked about technical cooperation with the United States, after President Donald Trump's announcement 10 days ago that it was 'terminating' its relationship with the WHO, said the WHO relies heavily on experts from the Centers for Disease Control and National Institute of Health. "We will continue to do that until we are otherwise instructed or informed."
AROUND THE WORLD
ASIA-PACIFIC
• New Zealand has became one of the first countries to return to pre-pandemic conditions on Tuesday, after declaring it was free of the coronavirus and lifting all social and economic restrictions except border controls.
• China has challenged US Senator Rick Scott to show evidence supporting his accusation that Beijing is trying to slow down or sabotage the development of a Covid-19 vaccine by Western countries.
• India's federal authorities struck down an order by the Delhi city government to reserve hospital beds for residents, and the country reopened shopping malls and restaurants even as it reported a record number of daily infections.
• Authorities in Pakistan have stepped up enforcement of safety measures after a rise in the daily number of infections pushed total cases above 100,000.
EUROPE
• The United Kingdom's quarantine will be struck down by the courts or dropped within weeks as some of Europe's biggest airlines prepare to file a legal challenge by the end of Tuesday, Ryanair boss Michael O'Leary has told Reuters.
• Moscow is lifting its months-long lockdown, mayor Sergei Sobyanin says.
• France's coronavirus deaths were four times higher on Monday than a day earlier but the increase of new confirmed cases of Covid-19 were at a one-week low.
AMERICAS
• US President Donald Trump is open to another economic relief package, White House spokeswoman Kayleigh McEnany said.
• Exactly 100 days after the first case was confirmed in New York City, some workers began returning to jobs at the start of reopening from a citywide shutdown.
• Brazil drew further criticism for its handling of the pandemic after it published contradictory figures on fatalities and infections, deepening a scandal over the country's Covid-19 data. The South American nation could see deaths rise to 165,960 by August, above the forecast for the US which has 100 million more people, according to a new projection by the University of Washington's Institute for Health Metrics and Evaluation.
• Venezuela's government said a flight carrying humanitarian aid for the epidemic had arrived from Iran.
• A US Navy investigation aboard the Theodore Roosevelt aircraft carrier has found that about 60% of sailors tested had antibodies for Covid-19, two US officials told Reuters, suggesting a far higher infection rate than previously known.
MIDDLE EAST AND AFRICA
• Children in South Africa began returning to classrooms as part of a gradual loosening of restrictions.
• Uganda's central bank again cut its benchmark lending rate by 100 basis points to support the economy as it downgraded projected growth.
• The pandemic has stymied a nascent rebound in sales in Egypt's private cement industry, raising the possibility of plant closures, industry executives and analysts say.
