Kenyatta National Hospital said on Twitter that 64 students were being treated at the medical facility for “various soft tissue injuries.” The hospital added that the medical team “has managed to contain the situation and the children are stable as they receive treatment.”

The cause of the collapse has not yet been determined, though commentators in local news outlets were quick to raise questions about the structural integrity of the building.

George Magoha, the education minister, said that the building was originally a single-level structure and the owners of the school had added the second level without approval. He added that if a request for constructing the higher floor had been submitted, it would not have been approved.

“If there was no other story put on top of that building, these innocent children would not have died,” he said during an afternoon briefing.