The Pershing County Sheriff's Office confirms ... they are investigating a death that occurred as rain poured down over the venue. The Sheriff has not gone into detail, but by the description, it might be rain-related.

As we reported, the event -- which was being held in the Nevada desert -- was flooded Saturday, causing cars and campers to become immobilized. It got so bad, concertgoers were told to shelter in place.

Diplo and Chris Rock fled the event on the back of a truck. Diplo said he walked 5 miles to get the hell out.

It's not looking better for Sunday ... they're expecting even bigger storms with heavy rainfall and hail, as well as 40 mph wind gusts.

Unclear if the plug has been totally pulled ... the gates to Black Rock City are locked up tight. No one can drive in the area except emergency vehicles.