And in Albany, Ga., a hospital executive was straining to send patients to other hospitals as the number of deaths doubled in a matter of days at the largest medical center in the southwestern part of the state.

While it ravages New York and metastasizes throughout much of the Northeast, the coronavirus is also quickly bearing down on new hot spots, sending doctors and first responders scrambling to prepare for the onslaught.

Still unable to conduct widespread testing, and fearful as the federal government fails to marshal critical supplies, officials in Boston, Detroit, Chicago, Atlanta, Milwaukee and Los Angeles are watching caseloads climb and taking extraordinary measures to prepare, all the while hoping that aggressive social-distancing measures might ward off the most dismal projections.

“I’m worried that New York might not be the worst-case scenario when you think about other states that have even older and less-healthy populations, and fewer hospital beds available,” said Retsef Levi, a professor of operations management at the Massachusetts Institute of Technology who has developed modeling tools designed to help public officials prepare for the spread of the novel virus and the disease it causes, covid-19.

Deborah Birx, the White House’s coronavirus response coordinator, said last week that the task force was anticipating challenges in parts of the country beyond the existing epicenters of New York and New Orleans, as well as Washington state, which reported the country’s first death from covid-19 last month.

She pointed in particular to Illinois’ Cook County, which includes Chicago, as well as Wayne County in Michigan, which includes Detroit.

The virus is spreading inland “following intense introductions into coastal areas,” said Joseph Eisenberg, professor and chair of the epidemiology department the University of Michigan’s School of Public Health.

International comparisons are scarce, he said, given the size of the United States compared with Italy or South Korea, and the reluctance here to enlist the “fairly draconian methods” used to contain the outbreak in China.

“Without sealing off borders, even just a few cases can seed transmission to a new state,” Eisenberg said. “Because Chicago and Detroit are important hubs, there also could have been introduction at various points in time, with the intensity now building.”

The danger is already being felt on the ground, where the rapid spread of infection in major metropolitan centers is driving up the numbers in Illinois and Michigan, which by Friday had reported 3,026 cases and 3,657 cases, respectively. The MIT modeling suggests that Northwestern Memorial Hospital, a premier center in Chicago, will be overrun once the infection rate reaches 3 percent — the figure reported in Italian cities as they began testing more consistently. At that level, the hospital, which is among those weighing a do-not-resuscitate policy for infected patients, would have about 1½ patients per intensive care unit bed.

Meanwhile, health officials warned that the virus would not respect city limits.

“It’s not like there’s a wall around Chicago,” said Allison Arwady, Chicago’s public health commissioner. “A lot of the patients we serve come from surrounding parts of the state, even other states.”

Faced with data showing the virus could quickly engulf the city and its surrounding suburbs, which had nearly 2,000 cases by the end of the week, officials were already taking steps to provide “mass care” reaching beyond traditional hospitals while also exploring “fatality management” that might include mobile morgues, Arwady said.

Emergency quarters planned for McCormick Place would hold patients with low to moderate symptoms to take the pressure off the city’s hospitals, she said. A spokeswoman for the convention center said the logistics had yet to be finalized, though the Federal Emergency Management Agency had already pledged $15 million to the Army Corps of Engineers for the project, according to representatives for both agencies.

The urgency is motivated in part by uncertainty about federal resources. The city has placed requests to the Strategic National Stockpile, but the amount of personal protective equipment it has received so far “was not even worth putting in our local spreadsheets,” Arwady said. She was looking elsewhere for assistance, including to local members of international disaster-relief organizations who might be able to supplement medical staff.

The sense of scarcity is widespread, even in places not yet experiencing shortages.

“We’ve looked in every corner, found every vent that we have, but very much are watching carefully, will we have enough vent technology to care for these patients,” said Ann L. Prestipino, incident commander for the covid-19 emergency at Boston’s Massachusetts General Hospital, which had 45 people on ventilators Friday, 26 of them for confirmed or suspected coronavirus cases.

The state’s numbers were climbing quickly. Between Thursday and Friday, Massachusetts identified 823 new cases, an increase of 34 percent that brought the state’s total to 3,240.

Prestipino, who also led Massachusetts General’s response to the 2013 Boston Marathon bombing, called the covid-19 emergency “bigger and more complicated than anything we’ve seen before.”

Boston’s mayor, Marty Walsh (D), said the city was planning for the “inevitability of overflow.”

Detroit, with more than 1,000 confirmed cases, was already reaching that point. Jenny Atas, a physician and regional medical director coordinating with 33 hospitals and 85 emergency medical services agencies, said hospitals in Wayne County were at capacity, as the virus reached its “tentacles to outlying counties.”

“We’re starting to get positive cases across the state,” she said. “It’s no different from New York or Washington state, really.”

Underscoring the precarious situation in Detroit, the Henry Ford Health System drafted a grim letter to patients and their families explaining the hospital’s calculations if it doesn’t have enough equipment to treat everyone.

“Some patients will be extremely sick and very unlikely to survive their illnesses even with critical treatment,” the letter explained. “Treating these patients would take away resources for patients who might survive.”

Among those who would not be eligible were those suffering severe heart, lung, kidney or liver failure, as well as those with terminal cancer. They would getpalliative care, the letter said.

Adnan Munkarah, Henry Ford’s chief clinical officer, said in a statement that the letter was a draft but that “with a pandemic of this nature, health systems must be prepared for a worst-case scenario.”

Hospitals throughout Michigan already have received instructions for splitting a ventilator between two patients in case the circumstances demand it, as they have in New York, Atas said. One emergency department in Wayne County, she said, has been closed and converted into a facility for victims of the virus, which has sickened 33 employees of the sheriff’s department, and killed one commander, according to a department spokeswoman, Pageant Atterberry.

It was another sign, beyond the toll on health workers, of the outbreak’s reach into the ranks of front-line officials charged with ensuring public safety. Four members of Chicago’s fire department have tested positive for the virus, according to a spokesman, Larry Langford. Many more are in isolation.

A spokesman for the New Orleans Police Department said 63 officers are either sick or quarantined — about 5 percent of the force. The city, which reached 1,298 cases by midday Saturday and has the highest covid-19 death rate per capita in the country, could run out of ventilators by early April, said Louisiana’s governor, John Bel Edwards.

Several days ago, the state ordered 12,000 of the lifesaving breathing devices — 5,000 from the Strategic National Stockpile, 7,000 from private vendors. “Today we have received exactly 192,” Edwards said Friday, with another 100 supposed to arrive next week.

Craig Coopersmith, a critical care surgeon in Atlanta who is managing Emory Healthcare’s coronavirus response across 15 intensive care units in six hospitals, said he was opening a new ICU just dedicated to the virus every few days. “The system is stretched,” he said.

Nearly 200 miles south of Atlanta, the virus is also overwhelming the rural community around Albany, Ga., a city of 73,000. The Phoebe Putney Health System there was under siege last week as the number of deaths jumped from 11 to 18 in about three days. Doctors and nurses, some bruised from face masks, were laboring 16- to 18-hour days, said Scott Steiner, the system’s chief executive.

Reinforcements were welcomed Friday in Los Angeles, where California Gov. Gavin Newsom (D) joined the mayor, Eric Garcetti (D), to mark the arrival of USNS Mercy, a 1,000-bed hospital ship deployed by the federal government.

The ship will serve those battling illnesses other than coronavirus to relieve pressure on hospitals treating covid-19 patients.

Los Angeles County health officials predict that hospitals could be overwhelmed within two weeks. At particular risk is the homeless population, which numbers about 45,000 living on the street in the county. The city is turning 42 recreation centers into shelters. Statewide, Newsom has arranged for more than 4,000 hotel rooms to be used for the homeless from Oakland to San Diego, but many have yet to be filled.

In Milwaukee, city officials were preparing to take over a convent to treat the homeless population showing symptoms of the virus. The city is quickly running out of beds, warned Mayor Tom Barrett (D), who said there were only about 4,000 available statewide. Wisconsin Gov. Tony Evers (D) said the Army Corps of Engineers was scouting locations for overflow facilities but had not settled on any sites.

Jared Polis, the Democratic governor of Colorado, said Friday he aimed to assemble 1,000 additional hospital beds by May, and another 5,000 by the summer. The state, which has 1,734 confirmed cases, is currently equipped with 900 ventilators and is estimated to need 7,000, the governor said.

In Denver, medical staff was already running low on protective equipment, said the mayor, Michael Hancock (D).

“If they get sick and can’t go into work, we’re in trouble,” he warned.

Boston’s Massachusetts General was treating 61 patients with confirmed cases Friday, but 89 of the hospital’s employees had already tested positive, with another 281 furloughed out of concern about their exposure.

Officials in these cities were watching their counterparts in New York and New Orleans, wondering if they soon would share their fate. While the virus seemed set to buffet population centers in Michigan and Illinois, “we don’t know what’s next because of a lack of data,” said Leana Wen, a former Baltimore health commissioner.

“We have no idea which communities are going to be the next hot spots and how many there are going to be,” she said. “A few months ago we saw the images coming out of China and a couple weeks coming out of Italy. We had time to prepare for this. We saw what happens to other places. This bought us time, but we didn’t use the time.”

David Montgomery and Richard A. Webster in New Orleans, Scott Wilson in Santa Barbara, Calif., Haisten Willis in Atlanta, Jennifer Oldham in Denver and Emma Brown contributed to this report.