CNN's Erin Burnett was floored on Wednesday's broadcast of "OutFront" by video of a catastrophic flash flood in Nepal that has left at least 150 people dead and more than 47 Americans missing.

Reports indicate that the flooding was caused by a half-mile-wide chunk of a glacier breaking off. CCTV captured footage of a wall of black, muddy water destroying buildings and cars as it tore through a town. Officials expect that toll to rise in the coming days, Burnett reported.

Burnett highlighted one segment that showed a seven-story building enveloped in water, looking as if "a bomb hit it."

"This is unforgettable," Burnett said. "You can't unsee that. You see that black wall of water? That looks like a bus depot of some sort, and it rolls through. And then, just as if they were matchbox cars, we don't even know how many innocent people's lives were lost in that instant."