Two buildings collapsed in a busy commercial strip of Center City in Philadelphia on Wednesday morning, leaving two reportedly killed with at least 13 people injured, the Associated Press reported. Officials said a search-and-rescue operation will remain active for at least 12 to 24 hours with the exact number of people who were inside the thrift store when it was destroyed remains unknown, news reports said.

The four-story building that was being demolished apparently fell onto the Salvation Army store in Central Philadelphia at about 10:45 on Wednesday morning, city Fire Commissioner Lloyd Ayers said. Thus far, 14 have been helped from the rubble with 13 taken to hospitals, officials said. Firefighters continue to determine whether others are trapped, as of Wednesday afternoon.

The building "collapsed the wrong way and landed on a thrift shop" that had people inside inside, CNN reported.

"Keep in mind we did not know, and we do not know, how many people were actually in the thrift store this morning when the wall collapsed this morning," Philadelphia Mayor Michael Nutter said.

"At this time, we are gathering information about the details of the building collapse at 22nd and Market Street in Philadelphia today. Our No. 1 concern is for the safety of our customers and the employees who were involved," Donald Lance, divisional Leader of the Salvation Army's Eastern Pennsylvania and Delaware Division said.

"We are coordinating with the police and fire Department, the Office of Emergency Management and local authorities," Lance continued. "Also, we have sent our own disaster response team to the site to serve survivors and first responders. We ask for the public to pray for those involved."