The cremators at Green-Wood Cemetery start their day at 6 a.m. They pull on gloves, masks and other protective gear, spray down caskets with bleach and ignite the cremation chamber, known as a retort. They hope for cardboard caskets – fancy lacquered wooden ones take longer to burn.

By the end of their 12-hour shift, they will slide 25 caskets through the cemetery's five retorts – more than twice the normal volume – and let the flames and 1,600-degree heat do their work. The shift is repeated seven days a week, nonstop, as the coronavirus delivers a steady stream of bodies to Green-Wood and other crematoriums around the country.

"It seemed like it went from zero to 60 in two seconds," Eric Barna, vice president of operations at Green-Wood, a historic cemetery in New York City's Brooklyn borough. "The numbers just skyrocketed."

Crematories across the nation are working long hours and double shifts to keep up with the increased death count from the coronavirus. As of early Monday, COVID-19 had killed more than 40,600 Americans, according to Johns Hopkins University data. Thursday saw the highest single-day spike yet, with 4,591 deaths reported. The U.S. has more confirmed COVID-19 deaths than any other country in the world.

Hospitals, coroner's offices and funeral homes have struggled with bodies overflowing their storage areas – a problem that often falls to crematoriums to ease.

New York City, which has recorded nearly 9,000 COVID-19 deaths, has faced the biggest struggle – partly because of the high numbers but also because of a state law that requires crematories be located only in cemeteries, said Barbara Kemmis, executive director of the Cremation Association of North America.

Because of the law, only four crematoriums serve New York City, a city of 8.3 million people that accounts for one-third of the nation's coronavirus deaths. To help meet demand, the state of New York recently loosened its regulations to allow crematoriums to operate 24 hours a day, seven days a week, Kemmis said. New Jersey passed a similar law this week.

But many of the older retorts can't run for 24 hours a day and need cool-down periods, she said. Meanwhile, many families are opting for cremations in the hopes of holding memorials for loved ones later when restrictions on funeral gatherings are lifted, she said.

"More people are choosing cremation because they can't have a funeral," Kemmis said.

Stephen Kemp, owner of Kemp Funeral Home & Cremation Services in the Detroit suburb of Southfield, Michigan, had to rent a 32-foot-long refrigerated trailer to store bodies awaiting cremation. The crematorium he usually contracts with is backed up with bodies, even though they've been working nonstop, he said.

"We have to make appointments for cremations," Kemp said. The crematorium "has a cooler (for bodies), but they're overflowing."

Before the outbreak, Professional Funeral Services in New Orleans' Treme neighborhood did mostly cemetery burials, including horse-and-buggy and traditional jazz funerals, even though it has a crematorium on site.

Since COVID-19 began sweeping through the city last month, restricting gatherings, requests for cremations have surged, owner Malcolm Gibson said. The number of cremations they perform using their one retort has soared from about 60 to 130 a month, the majority of them COVID-19 victims, he said.

The funeral home has had to store more than 60 bodies at its two locations. The home's seven licensed cremation operators are working 12- to 14-hour shifts to keep pace with demand, he said.

"It’s carnage," Gibson said, "to have this level of tragedy in such a short period of time."

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The outbreak has taken a personal toll on the funeral home: The office manager lost her dad to COVID-19, and one of the drivers lost his mom. Gibson buried his uncle last week, another victim of the outbreak.

"You take a minute, you cry, you reflect," he said. "But you know you can’t stay there. You have a high obligation to the families you're serving."

Workers at Green-Wood in Brooklyn would normally perform 60 to 70 cremations a week, with a refrigerated storage room able to hold about 25 bodies, Barna said. As the coronavirus ramped up in New York, their cremations crept up to 74 by the second week of March. During the last week of March, they cremated 126 bodies, he said.

Bodies overflowed the storage room. At one point, there were 60 bodies in caskets scattered throughout the crematorium, he said.

"We had so many bodies back there we couldn't take anymore," Barna said.

With the death toll on a steady climb, executives at Green-Wood had to put a cap on cremations at 25 a day. As of this week, the cemetery was booked for cremations through mid-May, Barna said.

In a squat gray building in a corner of Green-Wood's idyllic 478-acre cemetery, two operators work from 6 a.m. to 9 p.m., cremating the bodies. Founded in 1838, the cemetery is a National Historic Landmark and site of a key Revolutionary War battle, where Civil War generals and luminaries such as composer Leonard Bernstein and artist Jean-Michel Basquiat are buried.

Amid the outbreak, the cemetery has one again found itself in the midst of American history. Caskets arrive through the loading dock and are sprayed down with a water-bleach solution before they are wheeled toward the retorts.

"We treat every interment or cremation like it's a potential COVID-19 case," Barna said.

Most cremations these days are what's known as "direct cremations," where the casket goes straight from the hearse to the retort without ceremony, he said. The retort is heated to between 1,400 and 1,800 degrees, and cremations could take two to four hours to complete, depending on the size and material of the casket.

Cardboard caskets are preferred to wooden caskets, which take much longer to burn, Barna said.

"We have gently asked (funeral directors) to try to reduce the number of wood caskets they bring us," he said.

Once the body and casket are burned, the remains are transferred to a processing machine that pulverizes them into dust that is poured into a plastic bag and placed into a temporary box or urn.

If a retort burns hotter than normal, such as to burn a large wooden casket, it needs more time to cool down afterward, slowing the process, Barna said.

"We're doing our best to keep up with it," he said. "Hopefully, there's a light at the end of the tunnel at some point."

Outside New York City, workers at Ferncliff Cemetery in Westchester County, about 20 miles north of Manhattan, have been seeing a similar spike in cremations: from a normal average of around 65 a week to about 140 a week.

On one day – Tuesday, March 24 – they received 250 cremations requests before noon, forcing them to shut down requests and begin scheduling cremations, said Kevin Boyd, the cemetery's president. It was the first time in the cemetery's 118-year history that they had to do that, he said.

Many of their cremation requests are coming from New York City funeral directors trying to find a quicker turnaround time than the city crematories, he said. Ferncliff has closed a chapel adjacent to its crematorium to store bodies there waiting for cremation.

The Ferncliff staff has been haunted by the increase in bodies and cremations, Boyd said. Most troubling: knowing that many of these bodies were people who died alone in hospitals of COVID-19 and will be cremated alone, too, he said.

"This has proven to be, for most victims, a fairly lonely experience," Boyd said.

Follow Jervis on Twitter at: @MrRJervis.