Travelers from California and other hard-hit states are told to quarantine in the Northeast, joining a growing list.

The Midwest, which had been a national bright spot, is now seeing the beginnings of a surge in coronavirus cases.

The shift comes as the number of new virus cases in the United States has gone up 80 percent in the past two weeks, according to a New York Times database, a troubling trend for states that have been moving forward with plans to reopen.

More than 4,600 new cases of the virus were announced on Tuesday in Arizona, by far that state’s most in a single day, as Alaska, Georgia, Oklahoma and South Carolina also reported single-day highs.

And even states that had reported improvements are starting to see the number of new cases rise, causing governors to rethink their plans to get residents back to work.

“If the spread of this virus remained at a low level, more testing should show a lower positivity — there simply wouldn’t be as many cases to pick up with testing,” said Mr.

In the United States, daily cases are increasing after an extended decline.

While data is the backbone of this response, containing the outbreak depends on four core interventions: readily available testing, comprehensive contact tracing, timely isolation of known cases and quarantine to break the transmission.

Fauci, the nation’s top infectious disease expert, warned Tuesday that the number of new infections in the United States could more than double to 100,000 a day if the country fails to contain the surge that is now underway in many states.

Fauci made the stark warning at a Senate hearing on Tuesday where health officials spoke about the need to reassure people about the safety of vaccines.

Fauci also said school administrators should take into account virus activity in their areas when they consider reopening plans for the fall.

Seven in 10 Americans have said they would get vaccines against the virus if immunizations were free and available to everyone, according to recent polling, a number that health officials fear may not be enough to achieve “herd immunity,” a term that signifies that a vast majority of a population has protection against infection.

The virus has infected more than 9 million people and has been detected in nearly every country.

The United States is not on that list.

At the same time, citizens of approved countries who reside in the United States may not be allowed entry.

As infections surge in the South and the West, the governors of New York, New Jersey and Connecticut — three former hot spots in the Northeast — called on Tuesday for travelers from California and several other states struggling to contain outbreaks to quarantine for 14 days upon reaching their states.

Cuomo of New York, a Democrat, said that visitors from an additional eight states — California, Georgia, Idaho, Iowa, Louisiana, Mississippi, Nevada and Tennessee — would be required to quarantine for 14 days upon arrival in the state.

People traveling to New York from Alabama, Arkansas, Arizona, Florida, North Carolina, South Carolina, Texas and Utah had already been told to quarantine.

New Jersey and Connecticut are advising travelers from the 16 states to quarantine.

Charlie Baker, a Republican, announced on Tuesday that beginning on Wednesday, the state would no longer require travelers from Rhode Island, Connecticut, Vermont, New Hampshire, Maine, New York and New Jersey to do so.

Starting July 15, people traveling to Puerto Rico will be required to bring proof of a negative test taken within three days of their arrival, the governor announced Tuesday.

Anyone who doesn’t have one will be tested, and those who test positive will have to quarantine for two weeks, and must assume all medical and housing costs.

On Monday, the Department of Defense announced that it had lifted travel restrictions for service members to all but three states: California, Florida and Michigan.

Gavin Newsom said that four more of the state’s 58 counties would likely be added to a “watch list” of places where officials are monitoring troubling trends in hospitalizations and positive tests.

In other news from around the United States:.

More than 80 soldiers tested positive for the virus on Monday after three weeks of grueling survival training in North Carolina, according to a current Defense Department official and a former one, who spoke on condition of anonymity.

The roughly 110-person class was quickly quarantined at Fort Bragg in North Carolina, but those who tested negative for the virus were allowed to leave, the former official said.

The former official said the virus was most likely spread by an Army instructor who tested positive but continued to teach the course, known as Survival, Evasion, Resistance and Escape, or SERE school.

But as new outbreaks spike across the country and force many states to rethink their plans to reopen businesses, the program is closing down with more than $130 billion still in its coffers.

As college athletes have returned to campuses for voluntary, organized workouts in June, 33 Division I schools announced more than 200 positive tests from athletes.

Mnuchin said he expected a rebound in the second half of the year while Mr.

Powell warned that a surge in cases could set the recovery back and “undermine public confidence, which is what we need to get back to lots of kinds of economic activity that involve crowds.”.

assembly line in Arlington, Texas, as a health measure after a surge of cases in that area.

said they were discussing the concerns raised by the local.

Biden, the presumptive Democratic nominee, said “we need a president” — not a “cheerleader.” And he accused Mr.

Trump of failing to protect the American people from the virus.

The Biden campaign laid out a plan to fight the pandemic as cases rise in many states.

It said Mr.

Fauci will have full access to the Oval Office and an uncensored platform to speak directly to the American people — whether delivering good news or bad,” the plan said.

“The irony is, I think we’re probably communicating directly, in detail, with more people than we would have otherwise,” he said Tuesday, citing his many virtual appearances.

Late last month, 121 prisoners from the California Institution for Men in Chino, which had nearly 700 cases and nine deaths, were bused to San Quentin, where no inmates were known to have the virus.

Across the United States, the number of prison and jail inmates known to be infected has doubled during the past month to more than 80,000, according to a New York Times database.

Nine of the 10 largest known clusters of the virus in the United States are inside correctional institutions, The Times’s data shows.

The study showed that at the start of the quarantine, 73 residents of Vo’, or 2.6 percent of the population, tested positive for the virus.

Two weeks later, that number had dropped to 29 people, eight of which were new cases, but in both rounds of testing, 40 percent of the positive cases had been asymptomatic.

Prime Minister Narendra Modi of India announced on Tuesday that more than 800 million citizens would receive free food aid through the fall, in a move intended to mitigate hardship for those affected by the virus.

Airbus announced Tuesday that it would cut 15,000 jobs across its global work force, the largest downsizing in the history of the company.

Canada extended its ban on most travelers coming from places outside of the United States until July 31.

A separate measure barring people coming from the United States is in effect until July 21.

On Tuesday, Victoria recorded 60 new cases, its 14th consecutive day of double-digit increases.

Australia, with a population of 25 million, reported just seven cases in its other states on Tuesday.

A new strain of the H1N1 swine flu virus that has been circulating in China should be “urgently” controlled to avoid another pandemic, a team of scientists said in a new study.

Stranded in a crowded encampment along the Mexican border, migrants waiting to apply for asylum in the United States have for months feared that the coronavirus would reach them.

Two other people at the camp were isolated on June 26 after presenting symptoms of Covid-19, the organization said.

policy, known as the Migrant Protection Protocols, that requires asylum applicants to remain in Mexico while applying for asylum, entering the United States only on their court dates.

To date, there have been 1,215 confirmed virus cases in Matamoros and 2,183 cases in Cameron County, Texas, which have both experienced spikes in the last week.