This many people/These many people moving around ...

[Yb167]

Which one here is correct?

This many people moving around in very little space is making me dizzy.

These many people moving around in very little space are making me dizzy.

 

[teechar]

Both are grammatical.
The first is generic and just says "such a large number of people ... is making me dizzy".
The second is pointing to a particular group of individual people.