When there is a natural disaster such as an earthquake or tsunami, how are reporting outlets so quickly able to identify the number of lives lost?

I'm not suggesting it's an impossible thing to do or the numbers aren't legit. I've just always wondered how within hours they have a number to even start with. I just imagine devastated people trying to get themselves to safety and not even being sure of the condition of their loved ones yet. So how is this data being collected? What entity is in charge of this, and who specifically is reporting it to them?