NEW YORK (Reuters) - The daily tally of New York City residents who died at home with coronavirus-like symptoms exploded from 45 on March 20 to 241 on April 5, according to Fire Department of New York data - suggesting the city may be significantly undercounting COVID-19 deaths.

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Asked about the fire department numbers at a press conference Tuesday, New York City Mayor Bill de Blasio acknowledged that deaths at home haven’t been fully accounted for.

“It’s right to assume the vast majority are coronavirus related,” he said. “And that makes it even more sober in the sense of how many people we are losing, how many families are suffering, how real this crisis is.”

The fire department data are based on information collected during emergency calls involving cardiac or respiratory arrest, with fever and cough. Those are symptoms characteristic of a severe case of COVID-19, the disease caused by the coronavirus.

Although those symptoms also could fit diseases such as influenza, the steep rise coincides with the surge in COVID-19 cases in New York City, the epicenter of the U.S. coronavirus epidemic.

The data raise questions about the city’s official tally indicating coronavirus deaths had leveled off in recent days (before rising again Tuesday).

The official daily death count had stayed relatively flat, going from 309 on from March 31 to 290 on April 5, according the health department’s website. During that same period, according to the fire department data, the number of daily deaths at home among people with COVID-19-like symptoms rose from 167 to 241.

A spokesman for the city Department of Health and Mental Hygiene, which certifies findings on causes of death, said the official death count only includes those who had a test confirming they were infected with the virus.

The spokesman did not know what portion of people who died at home had been tested but said the department and the city Office of Chief Medical Examiner are working on counting the cases in which the deceased did not have a test.

The fire department would not comment on the significance of its figures, which first were reported on the website gothamist.com.

According to the data, a total of 2,192 at-home deaths were reported from March 20 to April 5. The city death count as of that day, including hundreds of deaths among the nearly 16,000 hospitalized for the disease, was about 2,500. It now exceeds 3,200.

Calls during the coronavirus outbreak in New York are swamping 911 emergency responders, the data show.

Between March 20 and April 5, the number of Covid-19-like cases, including patients who survived, tripled, from 94 to 322, according to fire department data.

The percentage of calls in which paramedics could not save the person rose from 48% percent to 75%.

“It’s never-ending,” said a fire department paramedic lieutenant who asked not to be identified. “And it’s getting worse each day.”

Before the coronavirus outbreak, the lieutenant said, the five boroughs averaged 10 to 20 calls a day that resulted in death.