The United States has now surpassed six million cases of coronavirus, according to data collated by Johns Hopkins University.
This is almost a quarter of the total number recorded across the entire world.
Johns Hopkins said the country, where more than 183,000 people have now died, added one million new infections in less than one month.
The total number of confirmed cases in the world is now more than 25 million, with more than 846,000 Covid-19 related deaths.
However, the true number of cases is likely to be significantly higher as many people who have had the infection but did not show symptoms have not been tested.
Elsewhere, the World Health Organization (WHO) warned that emergency authorisation of vaccines will require a "great deal of seriousness and reflection".
The UN body's chief scientist, Soumya Swaminathan, said every country had the right to approve drugs without full trials, but added that this is "not something that you do lightly".
The WHO confirmed that 33 potential vaccines are currently up for clinical trials, and that a further 143 are in pre-clinical evaluation.
On Monday, Johns Hopkins reported that there were now more than six million coronavirus cases across the US.
Johns Hopkins, which has been collecting US and global coronavirus data since the outbreak began in late 2019 in China, reported the first infection in the US on 21 January.
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The country reached its one-million mark in 99 days, on 28 April. Some 43 days after this, the number of infections doubled.
Three million cases were confirmed over the next 28 days, rising to four million on 23 July, after only 15 additional days.
The five-million mark was surpassed in another 17 days, and in 22 more days the six million mark was topped.
America remains by far the world's worst-hit nation in terms of the total number of cases and deaths, despite the number of daily cases declining.