More than 84,000 people were diagnosed with Covid-19 across the United States on Friday, according to a Reuters tally, a record one-day increase in infections during the pandemic as the virus surges again nationwide.

The spike to 84,218 cases, breaking the record of 77,299 set on July 16, comes as University of Washington researchers forecast that the US death toll from Covid-19 could reach a total of 500,000 by February.

Sixteen US states also hit one-day records for new infections of the virus that causes Covid-19 on Friday, including five considered key in the November 3 presidential election: Ohio, Michigan, North Carolina, Pennsylvania and Wisconsin.

Health experts have not pinpointed the reason for the rise but have cited such factors as colder temperatures driving people inside, fatigue with Covid-19 precautions and students returning to schools and colleges.