How to fix this?

Plumbers had to make this hole in my floor to access an old pipe under it. What you see through the whole is basically my neighbors ceiling. Apartment is from the 70s and im on the top floor. How should this be fixed properly? Some questions:

  • How can they build a base for pouring concrete?
  • Do they need to fix the rebar? (I see two rebars broken)
  • How long would the concrete take to cure?
  • How urgent is this? Like will the building collapse if I don’t fix this right away?