(CNN) — Two people are dead after a fire and explosion tore through a nursing home on the outskirts of Philadelphia on Tuesday, prompting local responders, bystanders and staff to rush the elderly residents to safety, Pennsylvania Gov. Josh Shapiro said. One of those killed was an employee and the other was a resident, Bristol Police Chief Charles Winik said at a news conference Wednesday. Twenty people were initially hospitalized, but one has since been released. One person is in critical condition. No first responders were injured, he said. Authorities had previously said some people were missing, but Winik confirmed all nursing home residents and employees have been accounted for. Officials’ preliminary belief is that a gas leak caused the explosion, Shapiro said at a news conference Tuesday evening. The investigation is being led by the National Transportation Safety Board, according to a statement Wednesday from PECO, the local utility company, which said, “It is not known at this time if PECO’s equipment, or natural gas, was involved in this incident.” The NTSB has a division that investigates accidents involving the transportation of natural gas. CNN has reached out to the NTSB for comment. Crews from PECO responded to reports of a gas odor in the facility shortly after 2 p.m., the company said in a statement Tuesday. “While crews were on site, an explosion occurred at the facility. PECO crews shut off natural gas and electric service to the facility to ensure the safety of first responders and local residents,” the company said, adding they are not sure whether their equipment or natural gas was involved in the explosion. First responders worked quickly to remove everyone they could find as they still smelled a heavy gas odor, Fire Chief Kevin Dippolito said Tuesday. About 15 to 30 seconds after firefighters left the building, there was another explosion and subsequent fire, he said, showing just how dangerous conditions were during the early rescue efforts. In addition to the fire, the building suffered major damage as the first floor partially collapsed into the basement, Dippolito said. On Wednesday, the fire chief said the collapse occurred in the part of the building where the cafeteria is located, with a utility area beneath it. He reiterated the origin of the explosion remains unknown. “The explosion was really quite catastrophic,” Shapiro said. Officials said it was a massive effort by everyone on scene to save people inside quickly, describing scenes of pulling people out of windows, staircases and elevator shafts. “There was one police officer who literally threw two people over his shoulders and ran with people to help,” Dippolito said. Bristol Health Rehab Center, formerly known as the Silver Lake Nursing Home, said in a Facebook post local authorities were responding to the facility and they would post updates when warranted. It is located about 20 miles northwest of Philadelphia in Bristol Township. Harry S. Truman High School is being used as a reunification center for those displaced by the fire, said Christopher Polzer, assistant superintendent of Bristol Township School District. As of Wednesday morning, authorities had used “heavy machinery” to remove the building’s collapsed ceilings and walls, Dippolito said. Officials describe heroic effort Tuesday’s fiery explosion drew an all-hands effort as neighbors flocked to help and officers from as far as three municipalities away showed up to lend rescue assistance. The explosion occurred at 2:19 p.m., immediately lighting up radios with calls of the disaster, according to Dippolito. Within minutes, firefighters were on scene and started pulling people out of the compromised building, he said. Aleen Schiavo, a neighbor of the nursing home, told CNN she ran to the scene after hearing a loud explosion. “I was lying in bed and I heard a big boom,” she said. “About two minutes later, a friend of mine called me and told me that the nursing home blew up, so I ran out of the house to go check because I have some friends that work there.” Videos and photos captured by Schiavo show fire and EMS personnel arriving at the scene, with debris scattered across the ground. Willie Tye, who lives nearby, told the Associated Press he heard a “loud ka-boom” and “thought an airplane or something came and fell on my house.” When he stepped outside, Tye said he saw “fire everywhere” and people fleeing the facility. Images from the scene show a large black plume of smoke billowing from the roof as emergency vehicles surrounded the building. “I’ve never seen such heroism,” Winik said Wednesday, describing how first responders ran into the building to pull people out while the smell of gas was still strong and walls looked like they were about to collapse. “They couldn’t walk; they were in wheelchairs. Some people couldn’t talk,” Winik said of the people rescued. “This could have been a much more serious catastrophe.” The people who were rescued “were being brought out by the fire department were handed off to the police officers, which came from every direction, and I believe every municipality around here and were literally carrying the patients,” according to Dippolito. First responders were able to rescue two people from the collapsed basement just before the second explosion, Dippolito said. That explosion and the subsequent fire “actually helped us identify where the leak was coming from in the basement, and we just prevented it from spreading into other parts of the building,” Dippolito said. Shapiro praised first responders, saying in the initial response to the incident, “You saw what real heroism is all about.” Nursing home recently changed ownership Bristol Health Rehab Center, where Tuesday’s fatal explosion took place, changed ownership at the beginning of December, Shapiro said. On December 10, the Pennsylvania Department of Health visited the facility, where a plan was put in place to “upgrade the standards at this facility,” he said. He didn’t elaborate on what upgrades needed to be made or the details of the plan. “That work will obviously continue with the new owners to ensure that they do what is necessary to keep residents safe at this facility and at the others where they are being taken to,” Shapiro said. State records show the state health department cited the nursing home for failing to comply with several regulations during its most recent inspection in October, before the facility’s ownership changed. The citations included failing to maintain portable fire extinguishers on one of the facility’s three floors, failing to maintain access to some stairways and a lack of “smoke barrier partitions” on two floors. The facility was issued no citations after a fire safety inspection in September 2024, according to Medicare.gov, but Medicare’s listing for the facility gives it a “much below average” rating. CNN has reached out to Bristol Health Rehab Center for more information on Tuesday’s explosion and on the plan. CNN has also reached out to the Pennsylvania Department of Health for more information. This story has been updated with additional information. ...read more read less