** my personal opinion only **
After making the scene safe for crews to enter (eg what caused the collapse ? Do we have another Gladstone incident), the 1st responders should aim to begin the 1st part of the '5 stages of Rescue' or CREST.
C = Clearance of surface casualties, reconnaissance & emergency rescue
R = Rescue of the trapped
E = Exploration of likely survival points
S = Selected debris removal
T = Total debris clearance.
One of the hardest tasks, even in exercises, is the Recce. But it essential to be done accurately, quickly and early...It is really difficult to keep moving to survey the other portions of the incident when a casualty screams at you to help them.
But you could have 20 people stuck behind a door behind movable debris, further on....
A mud map of the incident scene detailing access, risks and casuality locations really helps the incident controller.
Another task for first responders is to secure the scene so spectators do not become casualties. This can occur by spectators entering the incident area, spectators collapsing after seeing the incident, stress on relatives of casualties, etc, etc.
As seen in the USA bridge collapse, if you can organise the spectators they can assist in the 'clearance of surface casualties'. They can also assist comforting/first aid in your central location for all casualties outside of the incident area.
A USAR team will use a standard USAR wall marking system, which is internationally recognised & is taught in USAR cat 1 course. This will detail via a diagram if it is safe to enter a space or area, how many casualties removed, who did the recce and how many are still trapped. The markings will be drawn in orange paint (spray cans).
Unfortunately, depending on when, where & time that the building collapse occured, you might not save everyone. It will also depend on the type of collapse (eg pancake, etc).
The 'aim of rescue' is always "to save the maximum number of lives in the minimum time".