MORRISON, Colo. (CBS4) – Falling rocks hit at least seven people at a concert at Red Rocks over the weekend.

Concertgoers crowded Red Rocks for two heart-thumping nights, a spectacle party for the band “Sound Tribe Sector 9,” but under the intense bass beats, the thousands in attendance couldn’t hear the crisis occurring throughout the amphitheatre. Rocks from the venue’s north wall mysteriously began falling onto the crowd shortly before the show ended, sending paramedics scrambling to treat patient in the sea of dancing bodies.

“Send me another paramedic up here!” one official can be heard screaming on the venue’s emergency radio system. And then a short time later he yells, “We need two more paramedics!”

Another official calls for a bus to come pick up the injured.

“I got one wrist fracture coming to you and a hand fracture, both secondary. They’re rock injuries,” a paramedic is heard over the radio.

Victims stretched from the 50th row to the front of the stage.

Red Rocks officials say they aren’t sure exactly how the rocks fell.

“When you start hearing multiple reports of multiple people being injured, then you start thinking that the potential is here for something bad to have happened,” said Lt. Brendan Finnegan of West Metro Fire.

Finnegan said of the seven people hurt, four had to be hospitalized, and one was sent directly to the emergency room.

“We don’t know what happened. That’s still under investigation. Without having someone who actually witnessed the event, seeing where the rocks came from and how it happened,” he said.

Investigators are checking into whether a person could have climbed to the top of the rock wall and thrown the rocks. It’s also possible an animal loosened them.

Officials stressed the venue is safe. They said they checked the area for any issues before going ahead with an event commemorating the 9/11 10-year anniversary that took place during the day on Sunday. Still, loose rocks are clearly visible on the north wall and there are plenty of other rocks that fell at one point or another around the gallery.

A full investigation is expected to take place on Monday, and some, if not all of the victims will be interviewed.