The United States, the country hardest hit by the coronavirus, on Tuesday posted 60,209 new cases, a record for a 24-hour period, according to a tally from Johns Hopkins University.
The country was just shy of three million cases, at 2,991,351, the Baltimore-based university said in its latest data as of 8:30 pm (0030 GMT Wednesday).
The death toll stood at 131,362, with 1,114 additional deaths counted.
A senior US official said the United States has informed UN Secretary General Antonio Guterres of its intention to leave the WHO, effective July 6, 2021.
President Donald Trump has been critical of the WHO's pandemic response, accusing it of bias toward China and ignoring early signs of human-to-human transmission of the deadly virus.
The United States is the largest financial contributor to the WHO -- which leads the fight on global maladies from polio and measles to mental health -- providing $400 million annually.
Joe Biden, the presumptive Democratic presidential nominee, said Tuesday he would immediately reverse the decision and keep the US in the WHO if he defeats Trump in November.
Senator Robert Menendez, the top Democrat on the Foreign Relations Committee, criticized the Trump administration's move.
"To call Trump's response to Covid chaotic and incoherent doesn't do it justice," Menendez said.
Critics say Trump is seeking to deflect criticism from his own handling of the pandemic, which has killed nearly 131,000 people in the United States, by far the highest death toll of any nation.
Officials have said hospitals in some parts of the country are in danger of being overwhelmed, with many states hit particularly hard after they eased virus restrictions.
Texas -- one of the new US hotspots -- on Tuesday registered a new daily case total of 10,028, making it the third state after New York and Florida to hit the grim milestone.
Top infectious disease expert Anthony Fauci has warned the country is still "knee-deep" in the first coronavirus wave.
But Trump pounced on that comment Tuesday, saying the United States was "in a good place" and adding: "I disagree with him."
Experts are still struggling to understand Covid-19, and the WHO said it was open to new research after scientists lobbied for it to stress that the virus can spread through the air farther and for longer than initially believed.
There have been explosions of infections across the world, including Iran, which announced 200 new deaths on Tuesday.
Australia on Tuesday ordered five million people locked down in Melbourne, its second-biggest city, to combat a surge in cases.
"We can't pretend" the crisis is over, said Daniel Andrews, premier of Victoria state.
The restrictions in the Melbourne area will last at least six weeks, while Victoria state will be effectively sealed off from the rest of the country.
Cases are also surging in India and four new coronavirus field hospitals were opened on Tuesday in the financial capital Mumbai as the nationwide death toll jumped past 20,000.
