An explosion and fire at a Pennsylvania nursing home killed two women — one resident and one employee — and wounded 20 other people, officials said.

The “catastrophic” incident — possibly caused by a gas leak — unfolded Tuesday afternoon at the Silver Lake Nursing Home in Bristol, which is about 25 miles northeast of Philadelphia.

Of the 20 people hurt, 19 are still hospitalized on Wednesday, including one in critical condition, Bristol Township Police Chief CJ Winik said on Wednesday.

Bristol Township Fire Marshal Kevin Dippolito said parts of the first floor collapsed into the basement, trapping people inside.

All employees and all 120 residents of the facility have been accounted for, the police chief said.

Winick praised the “heroism” of the first responders, who he said ran into the building, despite the strong smell of gas, and evacuated residents, including some who couldn’t walk or talk.

“This could’ve been a much more serious catastrophe,” he said at a news conference on Wednesday. “The actions of everybody involved help preserve life.”

The cause of the incident remains under investigation, Dippolito said on Wednesday. Pennsylvania Gov. Josh Shapiro said on Tuesday that the preliminary belief was that a gas leak was responsible, and Dippolito said the source of the leak was in the facility’s basement.