New Jersey and Connecticut also had one-day highs in coronavirus-related deaths. Officials in the three states still saw reason for hope.

New York, New Jersey and Connecticut see one-day death spikes.

Five weeks into the coronavirus outbreak, officials in New York and New Jersey, the two states hit hardest by the pandemic, hoped that the number of virus-related deaths had reached a peak and would flatten or drop for a third straight day.

It did not happen.

Gov. Andrew M. Cuomo said on Tuesday that 731 people had died of the virus since Monday, the state’s highest one-day total yet by more than 100.

“Behind every one of those numbers is an individual, is a family, is a mother, is a father, is a sister, is a brother,” Mr. Cuomo said at his daily briefing in Albany. “So a lot of pain again today for many New Yorkers.”

New Jersey’s toll also hit a new one-day high on Tuesday, with 232 people dying of the virus since the previous day, Gov. Philip D. Murphy said. On Sunday and Monday, deaths in the state were in the double digits.

Connecticut also reported its biggest one-day increase in deaths on Tuesday, with Gov. Ned Lamont saying 71 people had died since the day before. By comparison, Mr. Lamont had reported 17 new deaths on Monday.

The three states together reported 1,034 deaths in a day, the first time that the region’s one-day toll topped 1,000.

More people have died in New York and New Jersey, by far, than in any other state. The two states together account for more than half of the virus-related deaths in the United States. New York’s toll was 5,489 as of Tuesday; New Jersey’s was 1,232. In Connecticut, where the virus appears to have been slower to spread, 277 people have died.

“It’s almost unfathomable, folks, when you think about it,” Mr. Murphy said.

Still, all three governors said there were signs that the virus’s spread was slowing.

Mr. Cuomo described death as a lagging indicator in the fight against the virus: People are often ill with it for a long time before they die, he said. By other measures, he said, the curve of infection was flattening in New York, even as the number of critically ill patients kept rising.

The number of virus patients in hospitals increased 4 percent since Monday, the fourth straight day that it had grown 7 percent or less after growing at least 20 percent a day for weeks.

The number of patients on ventilators in intensive-care units increased, too, but at the smallest one-day rate in weeks, up 2 percent since Monday.

As of Tuesday, there were nearly 4,600 patients on ventilators in New York, far fewer than pessimistic projections in recent weeks had said there might be. That has helped keep the state from exhausting its supply of ventilators.

In New Jersey, state officials said that about 1,651 people were in what they called “critical care” on Tuesday, up from about 1,500 patients on Monday. More than 90 percent of the patients in critical care, about 1,540, were on ventilators.

And as in New York, New Jersey officials noted that the numbers of people in critical care and on ventilators were far below their worst-case scenarios.

Mr. Cuomo, whose PowerPoint presentations have become an essential feature of his briefings, displayed a bar chart of hospitalizations that showed them clearly leveling off in recent days, with days in the near future labeled “projected plateau?”

For the number of people in hospitals to stop increasing, he said, New Yorkers must continue to vigilantly practice social distancing and other behavior that reduce the virus’s spread.

“To the extent that we see a flattening or a possible plateau, that’s because of what we are doing and we have to keep doing it,” the governor said.

Mr. Murphy said that while it appeared the curve of infection “may finally be flattening,” New Jersey residents needed to continue to stay inside or six feet away from one another.

Here are Tuesday statistics from New York, New Jersey and Connecticut:

New York:

Deaths: 5,489, up 731 from early Monday.
Confirmed cases: 138,836 statewide, up from 130,689 on Monday. In New York City, there were 76,876 cases, up from 72,181.
Hospitalized: 17,493 people statewide, up from 16,837.
In intensive care: 4,593, up 89 from 4,504 on Monday.

New Jersey:

Deaths: 1,232, up from 1,000 on Monday.
Confirmed cases: 44,416, up from 41,255.
Hospitalized: 7,017.
In critical care: 1,651, up from 1,505 on Monday.
On ventilators: 1,540.

Connecticut:

Deaths: 277, up from 206 on Monday.
Confirmed cases: 7,781, up from 6,906.
Hospitalized: 1,308, up from 1,221.

Virus deaths may be undercounted as more people die at home.

The official death figures, awful as they are, may not actually reflect the virus’s true toll Around the country, according to experts and officials, virus-related deaths are being undercounted because of inconsistent protocols and limited resources.

In New York City, the leader of the City Council’s health committee, Mark Levine, wrote on Twitter that people were dying at home at about 10 times the normal rate, presumably in large part because of the virus, but that many deaths were not being counted as virus deaths.

According to the news site Gothamist, the city medical examiner’s office has not been testing dead bodies for the virus and has instead referred what it considers “probable” virus deaths to the city’s health department.

But the health department counts only confirmed virus cases in its official death tally, Gothamist reported, suggesting that many virus deaths were being missed.

Asked on Tuesday about an increase in people dying at home, Mr. de Blasio said, “I’m assuming the vast majority of those deaths are coronavirus related.”

He added: “It’s understandable in a crisis that being able to make the confirmation is harder to do, with all the resources stretched so thin.” City officials, he said, were focusing their resources on “saving the next life.”

Still, he said, “We do want to know the truth about what happened in every death at home.”