More than 27,000 New Yorkers have died since March 11 — 20,900 more than would be expected over this period and thousands more than have been captured by official coronavirus death statistics.

New York City deaths by week Observed Expected Note: Weekly allocation of deaths since March 11, 2020, is an approximation based on how mortality data has lagged in the past. Recent data is provisional and may increase as more deaths are counted. · Source: New York Times analysis of data from the National Center for Health Statistics, Centers for Disease Control and Prevention; NYC Department of Health and Mental Hygiene.

As of Sunday, the city had attributed 16,673 deaths to coronavirus, either because people had tested positive for the virus, or because the circumstances of their death meant that city health officials believed the virus to be the most likely cause of death.

But there remains a large gap between the 16,673 figure and the total deaths above typical levels in the last six and a half weeks: more than 4,200 people whose deaths are not captured by the official coronavirus toll.

A review of mortality data in 12 countries showed that official death tallies have undercounted coronavirus deaths by tens of thousands.

The recent death count reached six times the normal number of deaths for the city at this time of year, a surge in deaths much larger than what could be attributed to normal seasonal variations from influenza, heart disease or other more common causes. The city’s largest mass casualty event in recent memory, the terrorist attacks of Sept. 11, 2001, claimed only a small fraction as many lives.

It is too soon to know the precise causes of death for New Yorkers in this period. Although many of the deaths not currently attributed to coronavirus may represent an undercount of the outbreak’s direct toll, the broader effects of the pandemic might have also increased deaths indirectly. Throughout the city, emergency rooms have been overcrowded, ambulance response has been slowed, and many residents might have been reluctant to seek medical care because of fears of contracting the virus. Hospitals around the country have reported reductions in admission for heart attacks, one sign that some people may be dying at home from ailments they would survive during more normal times.

New York City deaths above or below normal Note: Weekly allocation of deaths since March 11, 2020, is an approximation based on how mortality data has lagged in the past. Recent data is provisional and may increase as more deaths are counted. · Source: New York Times analysis of data from the National Center for Health Statistics, Centers for Disease Control and Prevention; NYC Department of Health and Mental Hygiene.

The measurements in our chart rely on a New York Times analysis of mortality data from the city’s Department of Health and from the National Center for Health Statistics at the Centers for Disease Control and Prevention. They capture the number of New York City residents who have died each week since January 2017. The total number of deaths for the period from the start of the outbreak through April 25 comes from the city health department. The way in which these deaths are distributed by week is an approximation based on how mortality data has lagged in the past.

Even with these high totals, the recent numbers in our charts are most likely an undercount of all deaths in the city. In normal times, death certificates take time to be processed and collected, and complete death tallies can take weeks to become final. But even if the current count is perfect, roughly 27,600 New Yorkers have died of all causes since the beginning of the epidemic. That’s about 20,900 more than is typical.