What is the first thing you should do when responding to an emergency call that water is leaking from a ceiling during a rain storm and the ceiling starting to sag?

The first thing you should do is ensure the safety of anyone in the vicinity, moving them away from the area under the sagging ceiling. Next, turn off the electricity in that area to prevent any electrical hazards. If possible, contain the leak by placing buckets or containers under the leak to collect water and prevent further damage. Finally, assess the situation to determine if immediate professional assistance is needed.