The wall of a downtown Philadelphia building collapsed onto a Salvation Army Thrift Store on Wednesday morning, causing six casualties. The four-story building was being demolished next-door to the Salvation Army, where an unknown number of shoppers were trapped inside by debris.

Fourteen people have been taken to the hospital for examination and treatment after being safely removed from the rubble. In a press conference Wednesday, Philadelphia Mayor Michael Nutter requested that the media focus on the tragedy at hand, rather than speculating about what may have caused the collapse - “our firefighters are actively engaged in a search and rescue operation. It is delicate; this is dangerous work.”

The number of people that were in the Thrift Store is still unknown, and firefighters are still searching for workers and customers who may be trapped inside. City officials say that people who were on the sidewalk nearby when the building collapsed could also be trapped by the debris.

Says the city’s mayor, “This is an active Salvation Army Thrift Store … it was in business … at any point in time, you wouldn’t necessarily know how many people would be in this store … we want to make sure that we have done everything we can to get out anyone who was in the store.”

Onlookers say they saw the wall adjacent to the Thrift Store begin to sway just after a support beam was removed from the building. Some who were nearby when the building collapsed told Reuters it was “ground-shaking,” allegedly strong enough to knock a man down on a nearby sidewalk.

There are currently no known demolition violations, and an investigation of the collapse is underway.