President Donald Trump has urged states to shun lockdowns as his Democratic rival Joe Biden said the pandemic could not be stopped by “flipping a switch”.
Continuing a whirlwind schedule of rallies in battleground states, Mr Trump also mocked mask mandates.
Mr Biden said Mr Trump’s handling of America’s worsening coronavirus crisis was an “insult” to its victims.
The Democrat has a solid national lead over the Republican president six days before the 3 November election.
But Mr Biden’s advantage is narrower in the handful of US states that could vote either way and ultimately decide who wins the White House.
More than 75 million Americans have voted early, nearly 50 million of them by post, in a record-breaking voting surge driven by the pandemic.
Virus deaths are rising in 39 US states and an average of about 800 people are dying daily nationwide.
White House coronavirus task force expert Dr Anthony Fauci told the BBC on Wednesday that Mr Trump’s political rallies were bound to spread Covid-19. He said gatherings of people not wearing masks or socially distancing were potentially superspreading events.
Infection rates are also rising sharply across Europe, including in the UK, France and Germany.
Global stock markets plunged on Wednesday amid fears that the pandemic could reverse tepid economic recoveries.