At least eight people died and numerous others were injured in what officials described as a surge of the crowd at the Astroworld music festival in Houston while rapper Travis Scott was performing.

Officials declared a “mass casualty incident” just after 9pm local time on Friday during the festival where an estimated 50,000 people were in attendance, Houston Fire Chief Samuel Pena 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 thereafter.

The fire chief said “scores of individuals” were injured.

Officials transported 17 people to hospitals, including 11 who were in cardiac arrest, Mr Pena said.

It was not clear whether all eight who died were among the 17 that had been transported to hospitals.

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, he said.

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

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

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,” Mr Pena 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 was near the front of the crowd and said it seemed 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,” Mr 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.”

Mr Pena said 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 centre 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,” Mr 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, 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.

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

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