At least two people were killed after a powerful explosion tore through a nursing home near Philadelphia on Tuesday, collapsing part of the building, triggering a major fire and trapping residents inside, authorities said.

Pennsylvania Governor Josh Shapiro said emergency responders rushed into the burning Bristol Health & Rehab Center in Bristol Township despite intense flames, a strong smell of gas and a secondary explosion, rescuing residents and staff.

Fire officials said crews remained in “rescue mode” hours later, using search dogs, heavy equipment and sonar technology to locate possible victims. As of Tuesday evening, five people were still unaccounted for, though officials cautioned some may have left with family members.

The blast occurred shortly after a utility crew arrived at the facility to investigate reports of a gas odor. While a gas leak is believed to be the cause, Shapiro said the finding remains preliminary.

Fire Chief Kevin Dippolito described chaotic rescue efforts, with firefighters pulling residents from windows, stairwells and elevator shafts. Two people were rescued from a collapsed section of the building.

Authorities have not released the identities of the victims or confirmed the number of injured. The 174-bed facility, formerly known as Silver Lake Healthcare Center, had recently been cited for safety violations during a state inspection.

Investigations into the cause of the explosion are ongoing.