A four-story Center City building that housed a day-care center was evacuated Monday morning after the beams beneath the first floor shifted and cracked, causing the ground floor of the property to become structurally unstable.

Shortly before 11 a.m., Philadelphia police and fire officials responded to an emergency call at 1134 Pine St. after occupants thought they heard an explosion. Nearly 20 children in the Eurokids Learning Center on the ground floor were evacuated, police said. Occupants in apartments above the day-care center did not have to leave, said Karen Guss, a spokesperson for the Department of Licenses and Inspections.

When L&I and Philadelphia Gas Works officials arrived, they found no leaks or evidence of explosion. Instead, they determined that the flooring system for the first level had failed. L&I deemed the flooring “unsafe," meaning it was significantly deteriorated but not at immediate risk of collapsing.

No injuries were reported.

The department believes the structural issues were caused by long-term rot and possibly termites, Guss said. She added that there is no evidence of construction problems or misuse. An investigation by the department is continuing, she said, and the director of the day care has been told to not reopen. Occupants of the housing units on the upper floors are allowed to remain.

“L&I wants the whole building to be assessed, to be cautious, but the near-term concern is limited to the stability of the first floor,” Guss said in an email.

Philadelphia has increasingly faced problems with structural instability, with numerous buildings deteriorating and collapsing. City officials have said aging and ill-maintained properties are partially to blame. According to 2017 U.S. Census Bureau data, more than 70 percent of Philadelphia’s housing units were built before 1960. Additionally, nearly 115,000 properties in the metropolitan area reported having a crumbling foundation or one that has an open crack or hole, according to 2017 American Housing Survey data.

According to L&I, the property owner has been directed to hire an engineer to look at the structural integrity of the building and determine how it can be made safe.