The United States has hit a six-month high for new Covid cases with over 100,000 new infections being reported, according to a Reuters tally, as the Delta variant ravages areas where people did not get vaccinated.

The country is reporting over 94,819 cases on a seven-day average, a five-fold increase in less than a month, Reuters data through Wednesday showed. The seven-day average provides the most accurate picture of how fast cases are rising since some states only report infections once or twice a week.

In the coming weeks, cases could double to 200,000 per day due to the highly contagious Delta variant, says top US infectious disease expert Dr Anthony Fauci.

"If another one comes along that has an equally high capability of transmitting but also is much more severe, then we could really be in trouble," Fauci said in an interview with McClatchy.

"People who are not getting vaccinated mistakenly think it's only about them. But it isn't. It's about everybody else, also."