At least two people were killed and others remain missing after an apparent gas explosion partially collapsed the Bristol Health and Rehab Center, also known as Silver Lake Nursing Home, in Bristol Township near Philadelphia on Tuesday afternoon.

The blast occurred around 2:15 p.m. while PECO crews were responding to reports of a gas odor, sending flames and debris into the air and prompting a large emergency response.

Authorities have declared the incident a mass casualty event, urging the public to avoid the area as rescue teams from Pennsylvania and New Jersey assist in search and evacuation efforts.

Family members and staff reported difficulty reaching loved ones inside, and one employee said a gas smell had been reported over the weekend, ABC 7 News has reported.

Governor Josh Shapiro confirmed the fatalities Tuesday evening as officials worked to evacuate residents to a reunification center at Truman High School.