HOUSTON (AP) — Officials in Texas say at least eight people are dead and several others injured in a crowd surge at the Astroworld Festival.

The surge broke out just after 9 p.m. Friday while rapper Travis Scott was performing, Houston Fire Chief Samuel Peña told reporters at a news conference.

“The crowd began to compress towards the front of the stage, and that caused some panic, and it started causing some injuries,” the fire chief said. “People began to fall out, become unconscious, and it created additional panic.”

The show was called off shortly after several people began suffering injuries.

Officials transported 17 people to the hospital, including 11 who were in cardiac arrest, Peña said. Many people were also treated at the scene at NRG Park, where a field hospital had been set up.

Approximately 50,000 people were in attendance at the festival, Peña said.

The fire chief added that officials did not immediately know the causes of death for the eight people who died. A medical examiner would investigate. 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.

Astroworld is a two-day music festival that was scheduled to take place Friday and Saturday in Houston. The event was sold out, according to the Astroworld website. Saturday’s performances have been canceled.

Event promoters had arranged for medical units to be on scene at the festival, however, once the crowd surge began, those units were “quickly overwhelmed,” Peña 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.”