It all went down Tuesday night in Miami, where Bella was leaving Swan restaurant to get in a waiting SUV ... of course, she was greeted with tons of paps on her way out. Nothing too crazy -- that is, until one paparazzo took a nasty tumble at Bella's feet.

Bella was quick to bend down and help her up -- even before her brawny security guard could -- and a few other gals who seemed to be rolling with BH also sprung into action.

It's a pretty sweet moment as Bella and co. made sure the woman -- and her expensive camera -- were okay. Fortunately, she was ... the lady admitted to being a klutz, and was back on her feet in a matter of seconds. The group even chatted for a bit afterward.

The funny part comes when the convo ends and the photog very much tries to get back into job mode as Bella is about to leave. She got the shot she wanted ... we think.