The US could soon see 100,000 new cases of coronavirus every day, the country's top infectious diseases expert has warned.

Dr Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, told a US Senate committee that the daily surge in cases could more than double if Americans don't start following public health recommendations.

"I am very concerned because it could get very bad," he said.

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Currently 40,000 new coronavirus infections are being reported across the country every day, but this could go up to 100,000 if Americans do not wear face masks and observe social distancing, he said.

Dr Fauci cautioned that there is no guarantee of a "safe and effective" vaccine for COVID-19 and urged people not to let down their guard ahead of Independence Day celebrations this weekend.

The infectious diseases expert, who has served six administrations, has been kept largely out of public view after Donald Trump repeatedly contradicted his advice on how to handle the virus.

Earlier, Democratic presidential candidate Joe Biden launched a blistering attack on Mr Trump's "historic mismanagement" of the pandemic.

Speaking in his hometown in Delaware, Mr Biden accused the president of "outright ignoring the crisis" following a rise in cases and lockdown measures being reintroduced in California, Texas and Florida.

Infections have more than doubled in at least 10 states, with an epicentre detected in Los Angeles, the country's second-largest city.

More than 126,000 Americans have died from coronavirus and millions have lost their jobs after businesses and schools shut down.

The US economy contracted sharply in the first quarter and is expected to plummet again in the April-June period.