BRISTOL TWP., Pa. – This Christmas Eve, the National Transportation Safety Board (NTSB) is sifting through the rubble left from a deadly explosion at a Bucks County nursing home.

It happened at the Bristol Health and Rehab Center, previously known as the Silver Lake Nursing Home, in Bristol Township on Tuesday.

Authorities said 52-year-old staff member Muthoni Nduthu and a patient are dead.

Officials said 19 of the 20 injured remain in the hospital Wednesday, with one in critical condition.

More than 24 hours later, local, state and federal investigators remain on scene trying to figure out what caused the building to explode and burst into flames.

“Until we excavate that area and remove the walls and roofs that collapsed, we won’t have any idea what may have occurred in there,” said Bristol Township Fire Rescue Chief Kevin Dippolito.

Officials called the mass casualty incident “sad and tragic”.

“To a vulnerable portion of our community and a nursing home,” said Bristol Township Police Chief CJ Winik.

Witnesses and neighbors recalled the frightening moments the nursing home on Tower Road fell before their eyes.

Reports of gas odor and two explosions erupted at the property after 2 p.m. on Tuesday.

Some witnesses said they jumped in to help their loved ones and strangers.

“The nursing home exploded,” said Willie Tye, a neighbor.

The community is left mourning.

“I’m hurt. This is my neighborhood, so, like, I feel like they are my family,” said another witness, who lives nearby. “I was scared. I thought it was an earthquake, to be honest with you.”

“I heard a loud sound.” Tye said. “I thought was something fell on top of my house.”

Tye said he put his life on the line to go into the scene.

“My brother-in-law lives there in the nursing home. He got out safe,” said Tye.

He also helped several others he just met.

“I went and came out and brought more beds out. Helped the officers take beds out,” said Tye.

Thanks to quick thinking by a number of witnesses and first responders, officials said all of the nursing home’s residents are accounted for.

“In the immediate moments after the explosion, you saw what real heroism is all about,” Pennsylvania Gov. Josh Shapiro said at a news conference.

Shapiro said new owners took over the nursing home this month. The facility was inspected two weeks ago, with plans to upgrade the building.

“That work will obviously continue with the new owners to ensure that they do what is necessary to keep residents safe at this facility,” Shapiro said.

Until then, local, state and federal authorities are investigating day and night, as the community rallies together.

“That’s my main thing. Make sure everybody is safe here on my street,” said Tye.

PECO crews said they shut off the facility’s natural gas and electric services for the safety of first responders and residents.

It’s not known if PECO’s equipment or natural gas was a factor in the incident.

The NTSB is investigating.