Houston authorities are investigating what officials described as a crowd surge that killed at least eight people and injured "scores" of others, turning the Astroworld Festival into one of the worst musical concert tragedies in U.S. history. Officials declared a "mass casualty incident" at 9:38 p.m. Friday local time during the festival at NRG Park, where an estimated 50,000 people were in attendance, Houston Fire Chief Samuel Peña told reporters during an overnight news briefing. The surge began around the time that rapper Travis Scott, a festival headliner, took the stage. "The crowd began to compress toward the front of the stage, and that caused some panic, and it started causing some injuries, said Peña. "People began to fall out, become unconscious, and it created additional panic." As first responders rushed to the scene, 17 people were transported to local hospitals, including 11 who were in cardiac arrest, the fire chief said. Many people were also treated at the scene at NRG Park, where a field hospital had been set up. About 300 people were examined at that site throughout the day, said Peña. Astroworld promoters had medical personnel and an emergency transport component at the festival, but "they were quickly overwhelmed" as the injury count mounted at "really a chaotic event," the fire chief said. #astroworldfestival #houstontexas