At least 16 died and 11 more have been injured during an accident that occurred at a Korean pop (K-Pop) concert in Seongnam, located a little south of Seoul.

The victims were atop a ventilation grate to get a better view of the concert, which included various Korean bands including the popular 4Minute, in the midst of a crowd of 700 in the outdoor concert. Though the exact cause of the accident has not been confirmed, reports say that it is due to the fact that the grate was unable to hold the weight of the 20-30 people that were standing on top. The victims fell down the height of the ventilation grate of about 65 feet.

“I heard a loud noise around the end of the concert, but I assumed it was just cheering. Then I heard people screaming for help,” Choi, a 15-year-old, told Yonhap News Agency in Seoul.

“There was a sudden, loud screaming, and when I turned, it looked like people were being sucked down into a hole,” another witness told YTN.

Those who were injured were rushed into four hospitals near the concert location, according to Yonhap. The local fire department told Korean media that twelve people died immediately at the scene, two died on their way to the hospital, and the remaining number may have passed away during treatment.