A single act of generosity was multiplied again and again this week after a good Samaritan paid for hotel rooms to shelter homeless Chicagoans from a historic and potentially deadly cold snap.

Donations of transportation, food and money flooded in after strangers learned that real estate developer Candice Payne had booked 20 hotel rooms at the Amber Inn motel.

“I had strangers from social media who are now lifelong friends helping me,” she told CNN.

Soon, the improvised group had booked 60 rooms for more than 100 people, including children and families, Payne said.

“I have people dropping by daily to help who have seen the story on Instagram,” she said. “They have volunteered money and time and cars because we had to get them to the hotel.”

“I also have a real estate brokerage, so some of the agents came out to help,” she said. “They cooked for the homeless, helping serving them.”

The crew’s first move was to evacuate a tent city near the Dan Ryan Expressway, where a fire caused by a propane tank explosion forced out dozens of residents, Payne said.

The Salvation Army had gotten a request to shelter about 70 people but later learned it wouldn’t be necessary because of Payne and her team.

“We are thrilled that they are safe and warm,” charity spokeswoman Jacqueline Rachev said.

It came amid news that at least 21 people have died due to subzero temperatures in the US, including a 69-year-old who was found frozen to death.

Police said a colleague found the body of William L. Murphy, 69, between two semi-trailers at FedEx’s East Moline, Illinois, facility when Moline hit a record low of -36 Celsius.

Rock Island County Coroner Brian Gustafson said Murphy’s death “appears to be medical or natural” but that an autopsy was scheduled for Monday to determine if the frigid temperature played a role.

“We are saddened by the loss of our team member and our sympathies go out to his family and friends,” FedEx said in a statement.

In Michigan, Ada Salna, 90, died after locking herself out of her home while she was feeding her birds and cats.

An 18-year-old University of Illinois student Gerald Belz, of Cedar Rapids, Illinois, also died in the extreme cold and was found behind an academic hall on campus.

The dangerous cold and heavy snow that hobbled the northern US this week has retreated, but not before exacting a human toll: including hundreds of injuries, including frostbite, broken bones, heart attacks and carbon monoxide poisoning.

In Illinois alone, hospitals reported more than 220 cases of frostbite and hypothermia since Tuesday, when the polar vortex moved in and overnight temperatures plunged to -34C or lower — with wind chills of -45Ce or worse in some areas.

By yesterday, the deep freeze had mostly abated, with temperatures climbing as high as -5 or 6 Celsius in Minneapolis and Chicago.