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.

Axar.az informs, citing AP, Pennsylvania Gov. Josh Shapiro said in a later news conference that emergency responders braved the flames, a heavy odor of gas and a second explosion 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, earth-moving equipment 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.

Shapiro said a finding that a gas leak caused the explosion was preliminary.

Authorities did not identify those who died and did not immediately know the total number of people injured.

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