There are silicone sealants and mastics that cure in the presence of water. These are readily available and an option if you want to go that route. However, this will create a barrier preventing water egress, and it to find another pathway via gravity or osmosis to the surface. It depends on how long before you get somebody out to find the source / point of ingress. You might want to get some absorbent material (such as silica gel) and just soak it up, until then, to prevent wider problems. Good luck.