The boom rattled his car and pulled at the pit of his stomach.

Caleb Marsh looked to his left as the cloud of dust and debris exploded into the crisp December sky, shrouding the quiet residential South Philadelphia street like something he’d only seen in the movies.

Then, he ran to help.

Four neighbors climbed on the burning rubble of the collapsed rowhouse, trying to free a person who appeared to be trapped in the house. From the street, more shouted for fire extinguishers — no match for the escalating blaze — attempting to tame the fire themselves as the stench of gas hung in the air.

Much remains unknown about Thursday’s explosion and three-alarm fire in South Philadelphia that left one person dead, another missing and presumed dead, three houses completely collapsed, and two others structurally unstable: what caused it, whose lives it claimed, how long it will take crews to clean up the wreckage. But what is known is that, even in the minutes after the explosion rocked the 1400 block of South Eighth Street, Philadelphians were ready to help.

As everyday citizens rushed toward the flames, the heat from the fire, once tolerable, grew stronger, almost unbearable. Bricks and metal and shards of glass littered the street where the quaint rowhouses once stood.

A woman looked out from the door of a house next to the wreckage, holding a baby.

“You’ve got to get out of here,” Marsh recalled telling her.

“I think everyone was kind of just shocked, and then there was this feeling of helplessness," Marsh recalled. “People were trying to do what they could, but I think there was a point where we realized, OK, this is out of our league."

Within minutes, firefighters replaced the group of civilians, tugging at the body trapped under the rubble amid the growing inferno that Fire Commissioner Adam Thiel would later call a “gas-fed fire.”

“It was literally a firestorm. In addition to crawling into that fire, the buildings were collapsing around them,” Thiel said. “It was beyond difficult conditions, just truly chaotic.”

The fire commissioner praised both the neighbors and fire crews who worked to aid the families affected by the blaze.

“We really saw the best of Philadelphia yesterday in the wake of this tragic event," Thiel said. “We had neighbors helping neighbors, and friends helping friends, and families helping families, a lot of folks who virtually risked their lives to try to help complete strangers.”

As Jen Leary, founder of the Red Paw Relief Team, patrolled the scene Thursday helping pets affected by the explosion, she said she was touched by the efforts of the South Philly residents — some who were displaced themselves.

Someone brought pizza to the displaced, who were sitting on the SEPTA bus-turned-heating station. People offered up their homes to those without a place to spend the night. A woman provided an open invite to her home-cooked dinner spread. One man extended his bathroom to anyone who needed it. Several people passed out hot coffee. Bottles of water flooded in for the residents and first responders. One displaced neighbor offered a ride to another family in search of a place to stay.

On Friday, local businesses collected toiletries, clothing, and monetary donations, while restaurants offered free meals for those displaced.

“All around, people were asking how they could help,” she said. "I’ve been on scenes like this before, and it’s a Philly thing, but it’s really a South Philly thing. It was a South Philly miracle. No one was going to be left out in the cold.”

Staff writer Ellie Silverman contributed to this article.