BRISTOL, Pa. (AP) — A thunderous explosion Tuesday at a nursing home just outside Philadelphia killed at least two people, collapsed part of the building, sent fire shooting out and left people trapped inside, authorities said.

Pennsylvania Gov. Josh Shapiro said in a news conference several hours after the explosion that at least two had been killed after emergency responders braved the flames and a heavy odor of gas to evacuate residents and employees.

Fire officials said they were in “rescue mode” five hours later, with responders still digging by hand and using search dogs and sonar to locate potential victims.

The explosion happened at Bristol Health & Rehab Center in Bristol Township, just as a utility crew had been on site looking for a gas leak.

A plume of black smoke rose from the nursing home, as emergency responders, fire trucks and ambulances from across the region rushed there, joined by earthmoving equipment.

Authorities did not identify those who died and did not know the total number of those injured after residents and employees were evacuated to hospitals.

Shapiro asked his fellow Pennsylvanians to take a moment to pray “for this community, for those who are still missing, for those who are injured, and for those families who are about to celebrate Christmas with an empty chair at their table.”

The town’s fire chief, Kevin Dippolito, said at the Tuesday evening news conference that there were five people still unaccounted for, but he cautioned that some may have left the scene with family members.

Dippolito described a chaotic rescue where firefighters found people stuck in stairwells and elevator shafts, and pulled residents out of the fiery building through windows and doors.