LODI, Italy — One infectious-disease doctor said coronavirus had hit "like a tsunami" at his hospital, where more than 100 out of 120 people admitted with the virus have also developed pneumonia.

Another hospital nearby is facing staff shortages as doctors have become patients.

Doctors, virologists and health-care officials on the front line of Italy’s battle against coronavirus, in more than a dozen interviews, described a health-care system stretched to its limits — a situation other countries may face as the virus spreads.

In an effort to cope, Italy is graduating nurses early and calling medical workers out of retirement. Hospitals in the hardest-hit regions are delaying nonessential surgeries and scrambling to add 50 percent more intensive-care beds.

“This is the worst scenario I’ve seen,” said Angelo Pan, the head of the infectious-disease unit at the hospital in Cremona, noting the prevalence of pneumonia complications. He said 35 patients in his hospital required intubation or mechanical ventilation to breathe.

Italy has been conducting extensive testing for coronavirus, including testing people who do not exhibit any symptoms of covid-19, the disease it causes. As of Tuesday evening, 2,263 people had tested positive. Of those, 1,263 were hospitalized, including 229 cases in intensive care. Seventy-nine people had died.

Experts say that although most covid-19 cases tend to be mild, the clusters in northern Italy are resulting in more severe cases because they are hitting an aging population with a high incidence of cancer and other underlying health issues — the demographic most vulnerable to the disease.

“The situation is quite bad in the epicenter of the outbreak,” said Giovanni Rezza, director of the infectious-disease department at the Italian National Institute of Health. “We have a very old population, they need hospital support and assistance, and it’s a very high burden for the hospitals in that area.”

As with the cluster in Washington state, virologists believe the virus had been spreading in northern Italy for weeks before anyone realized. The 38-year-old Italian who was the first to test positive in the Lombardy region, and who remains in intensive care, had not traveled abroad, and doctors initially sent him home from the hospital.

Once covid-19 took hold, hospitals in the region were quickly overwhelmed with cases. And, by that time, dozens of doctors and other health-care workers had become infected.

“The lesson is that you have to intervene very, very fast and in a very tough manner,” Rezza said. “Otherwise, you’ll have a high burden of disease that will jeopardize the health system. We cannot compromise.”

While being accused of being slow to detect the first case, Italian health authorities then took decisive action, locking down 50,000 people and testing thousands in an effort to contain the virus’s spread. Health officials say they hope to see those measures having an effect toward the end of the week. But Rezza said restrictions on movements and gatherings could be extended beyond the initial two weeks, to better assess whether they are working, while the containment area could be expanded.

He said that while containment of the virus might not be possible at this stage, it was still important to slow down its circulation. “The worst thing is to have a lot of cases in one place.”

That has been the case 20 miles east of Milan in the town of Lodi, where two floors of the hospital have been dedicated to its 250 coronavirus patients, with about 70 in critical condition. Doctors said that they have treated the outbreak like a “mass-casualty event,” made worse by the fact that their staffing levels have also taken a hit.

“This hospital managed to stand in a very complex situation,” said Enrico Storti, head of emergency and intensive care at the hospital. “Physicians, nurses, technicians are also infected, so they were forced to stay home.”

Italian health officials say about 10 percent of medical workers in the Lombardy region have been infected.

Costantino Troise, the head of the medical union Anaao Assomed, said medical workers accounted for about 5 percent of infections in Italy. He said recent funding cuts meant that even before the virus hit, the country had been facing a shortage of thousands of doctors and nurses.

At the hospital in Lodi, doctor Francessca Reali, 43, is now a patient after contracting the virus. She said her symptoms were mostly mild, though stronger than the flu. She surmised she contracted it in the days before health workers realized coronavirus was in the community and were working without extra protection.

“A lot of us are positive with coronavirus,” she said of the doctors in Lodi. “At least five.”

Coughing as he gave an interview over the phone, Massimo Vajani, the head of the local medical association, said he had been tested for coronavirus five days earlier and was awaiting results. Three of the four family doctors in the Lombardy town of Castiglione d’Adda were under quarantine, he said. “We need more doctors and nurses.”

Doctors were doing their best to assist patients remotely, he said.

Pan, at the Cremona hospital, said, “I think the system will cope, but it depends how things develop in the coming days.” Other services were suffering, he said.

While chemotherapy treatments have continued, nonessential surgery has been delayed and the HIV ambulatory service has been temporarily paused.

At the Lodi hospital, Giovanna Cardarelli was visiting her 92-year-old father, who had been admitted with heart problems just before the coronavirus outbreak struck.

He cannot be transferred for the minor surgery his condition requires until he tests negative for the virus, because other hospitals are worried about contagion.

“I’m not blaming anyone, but it’s very stressful,” Cardarelli said, removing protective shoe coverings and a gown by the door and washing her hands with disinfectant. “It’s been two weeks. He’s very depressed, and we are all tired.”

Daniele Bellocchio in Lodi and Claudia Cavaliere in Milan contributed to this report.