New Covid-19 cases in the US have risen to their highest level in two months, according to Johns Hopkins University, which is tracking the outbreak.
On Tuesday the US reported 34,700 new cases – the third highest daily tally since the US outbreak began, according to AP news agency.
States including Arizona, California, Mississippi, Nevada and Texas had record numbers of new cases, AP said.
Health officials say the coming weeks will be crucial to stem the outbreaks.
On Tuesday America's top infectious disease expert Dr Anthony Fauci told lawmakers there was "a disturbing surge of infection" and "increased community spread" in many southern and western states.
"A couple of days ago there were 30,000 new infections" in a single day, he said. "That's very troubling to me."
He told Americans to take social distancing measures, saying: "Plan A, don't go in a crowd. Plan B, if you do, make sure you wear a mask."
The US has recorded more than 2.3 million cases of the virus and more than 120,000 deaths.
Meanwhile Brett Giroir, the health department assistant secretary who oversees US diagnostic capacity, told lawmakers he expected the US would be able to conduct 40 to 50 million tests per month by autumn.
Which US states are seeing cases surge?
The overall number of infections in the US rose by a quarter last week, with 10 states reporting a rise in cases of more than 50%, according to Reuters news agency.
Arizona on Tuesday reported a record 3,600 new infections, hours before President Trump held a campaign rally in the city of Phoenix.
Phoenix's Democratic Mayor Kate Gallego said Mr Trump's event would not be safe and urged him to wear a mask.
But the president, who has so far refused to wear a mask, insisted at the event that the coronavirus "plague" was "going away" and again referred to the virus as the "kung flu", which the White House denies is a racist term.
Arizona officials warn that over 80% of hospital beds are currently being used, and that the healthcare system may be overrun in the coming days or weeks.
In Texas, where record numbers of people have been admitted to hospital for 12 days in a row, a children's hospital in Houston has begun admitting adult virus patients.
Texas Children's Hospital urged the public to "take responsible actions – practice appropriate social distancing, wear a mask or face covering anytime you leave your home".
Both Arizona and Texas were among those states that removed coronavirus restrictions early. Texas has temporarily revoked alcohol licences from several businesses that were breaking social distancing rules.
On Tuesday the governor of Washington state, Jay Inslee, ordered all residents to wear face masks in public after confirmed infections rose by more than a third the previous week.
"This is about saving lives. It's about reopening our businesses. And it's about showing respect and care for one another," Mr Inslee said.
Several US states and cities have instructed residents to wear face coverings.
California, South Carolina, Utah, Mississippi and Louisiana have also seen a surge in caseload and some governors have said they may be forced to announce new lockdown measures.
On Monday, Florida surpassed 100,000 cases. In the absence of a state-wide mask requirement, several cities and towns have issued their own orders mandating masks in public.
The European Union is reportedly considering banning US citizens from entering the bloc as it considers how to reopen its external borders.
What were President Trump's testing comments about?
Dr Fauci and other health expertRead More – Source