Travis Scott's Astroworld Festival show took a turn for the tragic on Friday as frenetic and panicked fans desperately tried to stop the concert amid a crowd surge that left at least eight people dead and scores more injured. Scott apparently noticed an ambulance moving through the crowd, stopped performing for a few moments, then promised to “make this mother**king ground shake,” and resumed the show. It’s unclear if he heard the crowd.

Another 11-second post starts with a closeup of Houston police officers and medics attending to a fan on the ground, while the audio captures a line of Scott’s song.

Houston Fire Chief Samuel Peña said the crowd “began to compress towards the front of the stage” which triggered panic and caused some injuries. Then “people began to fall out, become unconscious, and it created additional panic.”Seventeen people were taken to hospitals, including 11 who were in cardiac arrest, Peña said, and “scores of individuals” were injured.

It’s still not clear what triggered the mayhem, though Houston Police said they are investigating “rumors” of someone sticking people with drugs. Officials said that the 50,000+ crowd began to surge forward around 9 p.m. as Scott took the stage, and within a half-hour, the situation had turned deadly. In the aftermath, social media filled up with first-person stories from people who said they were caught up in the crushing crowd and witnessed multiple people getting hurt.

According to the Houston Chronicle, Scott stopped multiple times during his performance when he spotted fans in distress near the front of the stage. The rapper asked security to help them out of the crowd. Emergency vehicles, lights and alarms flashing, cut through the crowds several times, the paper says.

Scott took to Twitter on Saturday morning to issue a statement, saying that he would cooperate with any police investigation.

Some 50,000 people were attending the two-day outdoor event, which has now been canceled.