The total number of coronavirus cases reported in the US has passed 4 million, reflecting a rapid acceleration of infections.
It took the country 98 days to reach 1 million cases, but just 16 days to go from 3 million to 4 million, according to a Reuters' tally.
The average number of new US cases is now rising by more than 2,600 every hour, the highest rate in the world.
As the pandemic has spread widely over the country, moving from the early epicentre of New York, federal, state and local officials have clashed over how to fight it, including over how and when to ease social and economic restrictions aimed at curbing the infection rate.
Whether to order the wearing of masks, a common practice in the rest of the world and recommended by the federal government’s own health experts, has become highly politicised, with some Republican governors particularly resistant.
Hostility to the idea appeared to be dwindling this week, however, including from the Republican administration of President Donald Trump, who once dismissed mask-wearing as an effort to be politically correct.
Mr Trump, who faces falling poll numbers over his handling of the health crisis ahead of the November election, has long refused to wear a mask in public but this week encouraged Americans to do so.
While Trump did not issue a national mandate, US Assistant Secretary for Health Brett Giroir on Thursday cited the importance of masks in “turning that tide.”
“We have to do our mitigation steps: wear a mask, avoid the crowds," he told Fox News Network.
"We won’t see hospitalisations and deaths go down for a couple of weeks because of lagging indicators, but we are turning that tide."
He also said the time it currently takes to get coronavirus test results back needs to be reduced. The huge surge in infections has created a testing backlog.
Quest Diagnostics Inc, one of the nation’s biggest medical test companies, said on Thursday it expects to cut week-long turnaround times for Covid-19 tests by more than half to get to “acceptable” levels by September.
