New York City's death count has spiked to more than 10,000 after it reported 3,778 people who likely had Covid-19, but died without being tested.
Firefighters and paramedics had been recording drastic increases in deaths at home around the city, assumed to be caused by the virus.
The new figures, from the city's Health Department, mark a 60% rise in deaths.
In terms of per-capita death rate, New York City has now outpaced Italy - home to the highest death toll in Europe.
"Behind every death is a friend, a family member, a loved one. We are focused on ensuring that every New Yorker who died because of Covid-19 gets counted," said the city's health commissioner, Dr Oxiris Barbot.
The revised count brings New York's total virus fatalities to 10,367.
Why has this happened?
New York Governor Andrew Cuomo on Wednesday said that the Centers for Disease Control and Prevention (CDC) had changed guidelines for how coronavirus deaths were to be recorded.
"They want deaths, and then another category of probable deaths," Mr Cuomo said, to be administered by local health departments or coroners. He added that people who passed away outside of a hospital or nursing home may have been missed in previous counts.
Mark Levine, chair of the city's Heath Council that even these adjusted numbers were likely an undercount.
"There were an additional 3,017 deaths above normal levels in past month, not known to be connected to covid," he wrote on Twitter. "There is only one explanation for this increase: direct & indirect victims of the pandemic."
How does this affect the official death toll?
It's unclear. Mr Cuomo said the state will work with local agencies to publish revised numbers "as soon as we can".
As of yet, the coronavirus database from Johns Hopkins University - used as the definitive count by many US states and news outlets, including the BBC - has not changed its tally to include "presumed" deaths.
"While these data reflect the tragic impact that the virus has had on our city, they will also help us to determine the scale and scope of the epidemic and guide us in our decisions," Dr Barbot said.
What are other states doing?
Since the start of March - before New York City reported its first death - the CDC asked local governments to record "assumed" coronavirus infections on death certificates.
But so far, the application has been inconsistent.
Municipalities in Connecticut, Ohio and Delaware have begun to recorded cases where the infection is assumed but not confirmed with a test, Dr Barbot told the New York Times, while officials in California and Seattle only count virus deaths if proven with a positive test.