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New York City first responders are handling "tremendously high" call volumes, working multiple double shifts with back-to-back cases and suspected coronavirus patients going into cardiac arrest as the disease continues to sweep the city.

"Everybody's overworked. There're people who are working five doubles, five 16-hour tours," in one week, said a New York City Fire Department emergency medical technician who works in the Bronx.

"You get your two days off, but those days you're just sleeping the whole day because your body's recuperating from so much work," the EMT, who spoke on condition of anonymity, said Thursday.

"The call volume is tremendously high. I was on a double — it was job after job after job," the EMT said. "As soon as you hit that button saying you're in service, you're getting another job."

As of Thursday evening, there were more than 51,000 known coronavirus cases in New York City, with more than 1,550 deaths.

The EMT said the calls covered a range of medical issues, from people who had tested positive for the coronavirus and were experiencing severe respiratory issues to suspected coronavirus patients who were going into cardiac arrest and others with minor symptoms who were scared and wanted to go to the hospital.

Last week, a lot of people with minor symptoms called, but this week more suspected coronavirus patients were calling after having suffered cardiac arrest, the EMT said.

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The EMT said access to personal protective equipment was an ongoing issue and described disinfecting the ambulance with cleaning sprays and wipes after handling every suspected COVID-19 patient. First responders said they worried about exposing those suffering from non-coronavirus-related issues, such as unrelated heart attacks or bone fractures.

"If we were able to have extra surgical masks, we would give them one to try to protect, but there's not much we can do," the EMT said.

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Jim Long, a spokesman for the New York Fire Department, said that the department is following all local and federal guidelines on protective gear and that there are "medically appropriate " rules for using N95 and surgical masks to conserve supplies.

The EMT said calls from people with milder symptoms who did not require hospitalization were overwhelming the system. People who believe they have the coronavirus but are experiencing minor symptoms should call 311 or their doctors and leave the 911 lines open for patients with more severe issues, the EMT said.

"It is scary. Just know if you have mild symptoms, drink a lot of fluids, take medicine if you need, but try to control it at home," the EMT said. "If you feel if you're in severe distress, obviously call 911. That's why we're here."

In an interview with NBC News, the city's chief of emergency medical services, Lillian Bonsignore, said she had never before seen what EMTs and paramedics are facing in her 30 years in the profession.

"This certainly is unprecedented," she said Thursday. "It's making it incredibly difficult, because we're seeing so many sick, really, really sick, people over and over, and with this type of call volume there really is no chance in between to take a break or decompress."

Bonsignore said paramedics on the front lines were "doing a tremendous job, but they're fighting."

"We consider this a war, and they're our soldiers, and unfortunately they're not immune to this virus, and many of them are getting sick," she said, adding that about 23 percent of the workforce was out sick.

She also encouraged people to save calls to 911 for "true emergencies."

"All of our hospitals are very overwhelmed at this point," she said.

She said that while access to protective equipment was "certainly a concern for everyone," her department has enough to meet immediate needs and health agencies' recommendations, including those from the Centers for Disease Control and Prevention and the World Health Organization.

"We have enough for today, we have enough for tomorrow, we have enough for next week," she said. "If this thing takes another turn, we'd have to reassess that."

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New York Gov. Andrew Cuomo said Thursday that even with an influx of materials, "supplies are an ongoing challenge."

Anthony Almojera, vice president of the New York City Fire Department's EMS officers union, said last week that EMS services had been receiving record calls.

"Last night, we saw over 6,500 calls, the night before 6,400," he said. "The last week and a half, we've been at 5,000 or more every day. That's more than 9/11. In the last two days, we've set records."