Still, Hamel, 24, and his partner have not been alone. In a gesture of friendship, another young couple in their building has also effectively shut themselves off from the outside world in order to protect Hamel. They venture out only to pick up groceries, leaving the food outside his apartment in bags and disinfecting milk cartons with bleach wipes.

The arrival of the coronavirus has led to many similar arrangements in New York, a city usually famous for neighbors who mind their own business. People who until recently limited their interaction to a nod in the elevator are now knocking on doors, offering to fetch a prescription or an extra C-Town grocery special, or to act as contacts with older neighbors’ children in other states.

But in this particular crisis, as New York becomes the country’s epicenter of a virus that can be fatal, the danger of spreading infection has added a note of tension to what might otherwise be simple acts of generosity.

As offers of help proliferate across WhatsApp, Slack, laundry rooms and lobbies, and college students band together to grab groceries for older people, elected officials and others warn that selflessness might be putting vulnerable people at greater risk.

“There’s no doubt that New Yorkers want to help their neighbors,” said Carlos Menchaca, a Democratic councilman from Brooklyn, who is asking volunteers to wait for guidance from medical experts. “But before we self-activate, we need to pause and put together guidelines that allow us to do it in a safe way.”

People are sounding the same warning about safety from London to Minneapolis, as a so-called mutual-aid movement gains momentum around the world. Mutual-aid networks are a community-organizing tool often used after events such as natural disasters, and consist in neighbors serving each other in a building or a block.

Menchaca said he felt it was necessary to ask people to “pause” as he saw mutual-aid Google documents and intake forms pop up everywhere last week, while witnessing countless offers to help in his own neighborhood of Red Hook.

“We are trying to flatten the curve — in the city and the country — but a neighborhood has to think that way, too,” Menchaca said.

Mayor Bill de Blasio has applauded the efforts of New Yorkers to help each other. But a sense of alarm has grown in recent days as the number of confirmed cases of coronavirus in New York has increased. As of Tuesday morning, New York state had more than 25,000 cases, with almost 15,000 of those in densely-packed New York City.

The city’s health department said in a statement to The New York Times that New Yorkers could help each other most by connecting by phone and video to offer “emotional support.” If a sick neighbor needs groceries, the city advised to “leave them on the door step.”

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Javier López, the chief strategy officer with the Red Hook Initiative, a youth development organization, said the ways of helping that developed after Hurricane Sandy hit the neighborhood in 2012 have had to be “tweaked.”

Staffers from the initiative have been working through a list of 2,000 phone numbers for residents of the Red Hook Houses, one of the largest public housing projects in the city, to create a map for who might need help.

“But throughout the process,” he said, “there is hesitancy. This is not Sandy. This is different. It’s a different response. They’re checking in through social distancing.”

When it comes time to distribute food and supplies, he added, there will not be central collection spots as there were after Sandy.

Large volunteering organizations like New York Cares are also changing, requiring volunteers to meet certain health requirements, and community partners to have hand-washing stations and adequate spacing between staff.

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The question of how to help can be a complicated calculus.

“Having weighed things out, I worry more about our vulnerable population withering in the dark than the slight possibility of transmission,” said Kimi Weart, a Brooklyn resident who joined an effort in her building in Lefferts Gardens to help frail or older neighbors. Helpers there are trying to reach such people by phone, said Weart, a graphic designer. If they can’t, they knock on doors with their elbows, she said, then quickly move back 6 feet.

As the city has largely shut down and people have been asked to remain indoors, efforts to help beyond one’s own building have also increased, an expression of the perceived need for assistance in a city with 1.73 million residents over age 60, as well as the large numbers of people restlessly stuck at home, wishing they could do something.

Students sent home early from college helped create a website, Invisible Hands, to take groceries to the homebound. No-contact courier services modeled on those in Wuhan, China, have also surfaced. And New Yorkers are offering all manner of help on Facebook, Instagram, Nextdoor, and on new neighborhood Slack channels like #BedStuyStrong.

Some are offering child care, or help navigating Google classrooms. Others have collected monthly MetroCards for workers who still have to commute, and pooled rent money for the newly unemployed. In Manhattan’s Inwood neighborhood, one man offered to share his “Inwood Quarantine Sourdough Starter” so others could also bake their own bread.

Invisible Hands drew nearly 7,000 volunteers in just over a week, said Liam Elkind, a junior at Yale University and one of its creators. “People need food now, and we are trying to get them food as quickly as possible,” he said.

By Monday, Invisible Hands volunteers had delivered groceries and other goods to more than 250 homes. Elkind said recipients slide cash under the door to the volunteers, who sanitize the bags they are delivering. The service asks volunteers to follow guidelines issued by the Centers for Disease Control and Prevention, and to wear gloves and clean their delivery baskets.

After Elkind delivered groceries to one woman in her 70s, he said, she invited him in for cookies and tea. “I said, ‘No, this is the opposite of what this is about!’ The whole point is we are minimizing physical contact.’”

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Organizations that bring food to homebound people, such as God’s Love We Deliver, City Harvest, and City Meals on Wheels, have said that while demand has increased recently, the volunteer pool has shrunken, in part because volunteers are usually older New Yorkers.

Rep. Alexandria Ocasio-Cortez, Democrat of New York, has encouraged people to create mutual-aid networks in their buildings or blocks — creating “pods” of neighbors — to bridge the gap.

“It’s really important because we can choose to share instead of hoard,” Ocasio-Cortez said on a recent call to promote the idea. Would-be helpers were encouraged to grocery shop during off-peak hours and to avoid public transit and face-to-face exchanges, tips her office said were consistent with the city’s public health guidance. A “tool kit” that was distributed after the call also suggests that people avoid touching doorbells with their fingers.

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In Brooklyn, Emily Claypoole has taken such precautions when she shops for her neighbor, Hamel. They knew each other in college but ended up in the same Bedford-Stuyvesant building by coincidence last year, she said. Now, they are connected in ways neither could have imagined.

Claypoole, who just lost her serving job at a Manhattan restaurant, sanitizes her hands often while making grocery runs, and wipes down packaged items with Clorox wipes before leaving the bags outside Hamel’s door. She covers her hand with her jacket sleeve or a cloth when opening doors. Helping her neighbor “has been a pleasure, it has not been a burden,” she said.

“The thing I would caution against is doing it out of guilt,” said Claypoole, 24. “Just because you’re not symptomatic, doesn’t mean you can’t pass it along.”

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Hamel, who described himself as “an extrovert to the heart and core,” is hunkering down patiently with his partner, Alex Harwood, and their cat, Basil. He urged well-meaning volunteers to think about the real danger they could pose to people like himself, especially when the medical system is becoming more strained.

Claypoole said that because of Hamel, she and her boyfriend skip random jaunts to the corner store for a forgotten item, and forgo all but the most important outings. “We are even more cautious,” she said, “and it even feels like that’s helpful for me and my boyfriend, and the community at large.”

This article originally appeared in The New York Times .