Snoop Dogg & Wiz Khalifa fans went down hard Friday night after the front-row railing collapsed at their show ... sending some to the hospital.
The rappers were performing in Camden, New Jersey ... you can see from the video fans were packed like sardines into the venue. The front rail gives out without warning, triggering a domino effect.
We're told at least 40 were hurt and some taken to a hospital.
The show abruptly ended.