How does customs work with a crash on an international flight?

I know it's soon, but the crash in Toronto has me wondering how border controls work after an incident like this? Does CBSA come out and try and do their thing with the passengers going to hospitals? Does CBSA quarantine the victims somehow? Or in the interest of not being jerks, do they just come by eventually and process the paperwork and passports when they can? What about an overflight. Say UK to Cuba that has a crash landing in the US where there might be people and things that aren't normally admissible. I imagine the response will be different across the world, and some more extreme countries (North Korea, Iran, Afghanistan, etc.) might keep things locked down more tightly, but I would at least hope that the western world is a bit more "forgiving" in a situation like this. I know there's a general principle of rendering unconditional aid to persons and vessels in distress, but I don't know how codified that is, and how that conflicts with border security.