Trying to remember a sci-fi film from 50s or 60s

I don't remember too much about it other than a few key shots. I'm unsure whether it was black and white, but it had people walking off in the distance on either farmland of fields and then suddenly falling through the earth, you just saw one individual at a time sort of disappear. And the end of the movie it's discovered an alien base or space ship is underground, the people running round are all wearing jump suits (you can see the zip up the back) it was called something like earth vs mars or something to that effect.