WASHINGTON: Dr. Anthony S. Fauci told Congress on Tuesday that he was seeing a “disturbing surge” of infections in some parts of the country, as Americans ignore social distancing guidelines and states reopen without adequate plans for testing and tracing the contacts of those who get sick.

Fauci’s assessment, delivered during a lengthy hearing before the House Energy and Commerce Committee, painted a much grimmer picture of the coronavirus threat than the one given by President Donald Trump, who claimed last week that the virus that had infected more than 2 million Americans and killed more than 120,000 would just “fade away.”

“The virus is not going to disappear,” said Fauci, the nation’s top infectious disease expert, who testified that the virus was not yet under control in the United States.

His testimony came as more than half of the country was seeing an uptick in cases, with officials in some states slowing their return-to-work plans or even imposing new restrictions. Fauci and three other leaders of the government’s coronavirus response who testified Tuesday cast a cloud over the sunny accounts offered by the president as he has portrayed the United States as a nation bouncing back from the brink.

“I am very cautious and I don’t — still don’t sleep well at night,” said Adm. Brett P. Giroir, the assistant secretary for public health, “because we have a long way to go.”

More than three months after Trump declared an emergency because of the virus, Fauci said the picture was a “mixed bag,” with some bright spots, but also some dark ones and many unknowns. Some states like New York are “doing very well” in controlling the spread of the virus, but the surge in other states is “very troublesome to me,” he said.

“The next couple of weeks are going to be critical in our ability to address those surges that we are seeing in Florida, in Texas, in Arizona and other states,” Fauci added.

The hearing came as the nation was still facing steep challenges in dealing with the virus. Giroir conceded that even the 500,000 tests the country was conducting daily were insufficient.