The gap between three million and four million is so far about 16 days.
It comes as the United States approaches four million total cases, with just over 70,000 new cases recorded in the most recent figures from the Centers for Disease Control and Prevention.
Some media, such as the New York Times, claim the figure has already passed four million.
States across the United States are seeing increases in cases following the easing of lockdowns over the course of a few months.
The southeast of the country appears to be particularly badly affected, with states such as Florida, Louisiana, Mississippi and Texas all having recently seen large increases in new cases, according to reports.
According to the most recent New York Times figures on average daily infections for the past week: Florida reported 11,116 – a 20 percent increase from two weeks earlier; Mississippi reported 1,215, a 70 percent increase; and Texas reported 10,012, an increase of 29 percent.
READ: POTUS admits schools can’t reopen as cases approach four million
This week alone, the president indirectly called the wearing of a face mask “patriotic” in a tweet, adding “there is no one more patriotic than me, your favorite president!
The President appeared earlier this month wearing a face mask for the first time during a visit to Walter Reed National Military Medical Center in Maryland.
Mr Trump had previously said he “didn’t want to give the press the pleasure” of seeing him wear a face mask and retweeted a social media post from Fox News host Brit Hume mocking the Democratic presidential opponent Joe Biden for wearing one.
Mr Trump has also canceled parts of a major Republican event – the Republican National Convention – due to take place in Jacksonville, Florida next month due to coronavirus fears.
US news site CNBC called the announcement a “staggering turnaround” for the president, given he criticized North Carolina Gov. Roy Cooper for making a similar move in May.
According to data from Johns Hopkins University on Wednesday, Brazil and India are behind the United States in terms of total number of cases, with 2,227,514 and 1,238,798 cases, respectively.