New surge in US cases
The US has seen record numbers of new cases in recent days and top health official Dr Anthony Fauci says there is a "serious problem".
So far, the US has recorded about 2.5 million cases of the virus and more than 125,000 deaths.
US health officials say
at least 20 million people in the US may already have been infected with coronavirus, according to latest estimates.
The Centers for Disease Control (CDC) said the figure - 10 times higher than the reported number - was because testing was restricted to people with symptoms and asymptomatic carriers were not tested.
Cases and deaths in the US had appeared to peak in late March, but by May, cases were declining and most states had begun to end restrictions and reopen businesses.
But a number of states reported record daily coronavirus infections this week and Texas and Florida have tightened restrictions on business again.
The University of Washington predicts 180,000 US deaths by October - or 146,000 if 95% of Americans wear masks.
The White House has said the rise in cases is a product of an uptick in US testing capacity. But Dr Fauci has warned that
higher percentages of positive tests in some states "cannot be explained by increased testing".
Governors across the US have been eager to reopen their states because of the dire effect the pandemic has had on the economy.
More than 45 million people in the US have applied for unemployment benefits at some point since March, with the downturn officially being declared a recession earlier this month.