HOUSTON (AP) — Fans attending a Houston music festival surged toward the stage during a performance by rapper Travis Scott, triggering panic in the crowd of tens of thousands. At least eight people were killed and many more hurt, authorities said.

The chaos unfolded Friday evening at Astroworld, a sold-out, two-day event at the NRG Park stadium. An estimated 50,000 people were in attendance. It was not clear what set the crowd in motion.

“The crowd began to compress towards the front of the stage, and that caused some panic, and it started causing some injuries,” Houston Fire Chief Samuel Peña told a news conference. “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.

Event organizers had arranged for medical teams to be at the festival. But once the crowd surge began, those teams were “quickly overwhelmed,” the fire chief said.

In a video posted to social media, Scott could be seen stopping the concert at one point and asking for aid for someone in the audience: “Security, somebody help real quick.”

Houston Police Executive Assistant Chief Larry Satterwhite, who was near the front of the crowd, said the surge “happened all at once.”

“Suddenly we had several people down on the ground, experiencing some type of cardiac arrest or some type of medical episode,” Satterwhite said. “And so we immediately started doing CPR and moving people right then.”

Satterwhite said he quickly met with promoters, who agreed to end the event “in the interest of public safety.”

Amy Harris, a freelance photographer for The Associated Press, described an “aggressive” crowd atmosphere throughout the day because of the way fans were behaving — pushing and rushing the stage barricades and prohibited VIP and admission areas.

“It was definitely the most chaotic festival environment that I’ve been in,” Harris said. “I felt uneasy all day.”

Houston Police Chief Troy Finner called for calm and urged people not to jump to conclusions about what caused the surge.

“I think it’s very important that none of us speculate. Nobody has all the answers tonight,” Finner said.

“We’re going to do an investigation and find out because it’s not fair to the producers, to anybody else involved, until we determine what happened,” he said.

It was not clear whether all eight who died were among the 17 people who were taken to hospitals. Many people were also treated at the scene, where a field hospital had been set up. About 300 people were examined at that site throughout the day, the fire chief said.

Authorities did not immediately know the causes of death, and the dead were not immediately identified. A medical examiner planned to investigate.

Scott, one of music’s biggest young stars, released two new songs earlier Friday, “Mafia” and “Escape Plan.” The 29-year-old Houston native has been nominated for eight Grammy Awards. He has a 3-year-old daughter with Kylie Jenner, who announced in September that she’s pregnant with their second child.

Drake joined Scott on-stage at the concert — which was livestreamed by Apple Music — and posted photos to Instagram after the performance.

A representative for Scott did not immediately respond to an inquiry from the AP.

Officials set up a reunification center at a hotel for family members who had not been able to reach relatives at the event. Authorities sought to connect families with festivalgoers who were taken to the hospital, “some as young as 10” years old, said Harris County Judge Lina Hidalgo, the county’s top elected official.

Scott founded the Astroworld Festival in 2018, and it has taken place at the former site of Six Flags AstroWorld each year since, except for 2020 because of the coronavirus pandemic.

The deaths called to mind a 1979 concert by The Who where 11 people died and about two dozen were injured as thousands of fans tried to get into Cincinnati’s Riverfront Coliseum.

Other music events that resulted in fatalities in recent years include the Las Vegas shooting massacre in 2017, when a gunman perched in a hotel window killed 58 people at the Route 91 Harvest Festival, the so-called Ghost Ship fire in 2016 that killed 36 people in a California warehouse during a dance party and a 2003 nightclub fire that killed 100 people in Rhode Island.

“Suddenly we had several people down on the ground, experiencing some type of cardiac arrest or some type of medical episode,” Satterwhite said. “And so we immediately started doing CPR, and moving people right then, and that’s when I went and met with the promoters, and Live Nation, and they agreed to end early in the interest of public safety.”

Peña said officials did not immediately know the causes of death for the eight people who died. A medical examiner would investigate. It wasn’t clear whether all eight who died were among the 17 that had been transported to hospitals. The deceased had not been identified as of early Saturday.

Officials set up a reunification center at a hotel for family members who had not been able to reach relatives who had been in attendance at the event. Authorities were looking to connect families with festivalgoers who were transported to the hospital, “some as young as 10” years old, Harris County Judge Lina Hidalgo said.

Houston Police Chief Troy Finner called for calm and urged people not to jump to conclusions as to what caused the surge.

“I think it’s very important that none of us speculate. Nobody has all the answers tonight,” Finner said. He added that there have been several rumors surrounding the event that authorities would look into.

“We’re going to do an investigation and find out because it’s not fair to the producers, to anybody else involved, until we determine what happened, what caused the surge,” he said. “We don’t know, but we will find out.”

The Associated Press reached out to a representative for Scott but did not immediately hear back.

Finner told reporters that Scott and the event promoters cooperated with police.

The deadly surge was the most deaths at a U.S. concert since the 2003 Station nightclub fire that killed 100 people in Rhode Island.

Eleven people died and about two dozen were injured in 1979 at a concert for The Who as thousands of fans tried to get into Cincinnati’s riverfront coliseum.