At least 20 million people in the United States may have had COVID-19, according to the Centres for Disease Control and Prevention (CDC).
"It’s clear that many individuals in this nation are still susceptible," said Dr Robert Redfield, director of the CDC, on a call with reporters.
"Our best estimate right now is that for every case that's reported, there actually are 10 other infections."
The current number of confirmed cases in the US is 2.4 million but the CDC estimate would mean that the true number of people infected in the United States is roughly 24 million people or 7% of the US population.
The estimate is based on serologic testing for antibodies in the US and comes as cases soar in a number of Southern and Western states.
These increases prompted New York, New Jersey and Connecticut, states that have lowered their epidemic curves, to require people travelling from Alabama, Arkansas, Arizona, Florida, North Carolina, South Carolina, Texas and Utah to self-isolate for 14 days when travelling to the three northeastern states.
Meanwhile, US President Donald Trump has insisted that the rise in cases is due to increased testing, which officials say is only partially true.
In some areas, increased hospitalisations and new record rises in cases show that the US is still engulfed in a large virus outbreak.
Trump recently held a rally in Phoenix, Arizona, a coronavirus hotspot, where images showed a packed gathering with few people wearing masks and no social distancing.
In some areas of the country, "we're now seeing a disturbing surge of infections that looks like it's a combination but one of the things is an increase in community spread and that's something that I'm really quite concerned about," said Dr Anthony Fauci, the US' top infectious diseases expert, on Tuesday while testifying before a congressional committee.
Officials say many of these cases are asymptomatic as well, citing concerns about silent virus spread that's difficult to catch despite the US' 500,000 daily laboratory tests.
Data compiled by the New York Times shows coronavirus cases increasing in 29 US states. Some states have halted their reopening plans due to the spread.
The US currently has the highest total death toll in the world with more than 124,000 deaths due to COVID-19.
The epidemic situation in the US prompted the European Union to include the US on a draft list of countries not able to travel to the bloc once external borders reopen.