Travis Scott says he's devastated after 8 killed at Astroworld music festival in Houston

A criminal enquiry has been ordered by Houston authorities, after pandemonium unfolded on Friday evening at Astroworld, during a music festival by rapper Travis Scott.

A stampede of fans surging toward the stage during Travis Scott's performance, which left at least eight people dead and dozens more injured.

As fans pressed toward the stage, people began to fall unconscious, some apparently suffering cardiac arrest or other medical issues.

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The two-day event was sold-out, with an estimated 50,000 people in attendance. Some unconfirmed reports say that someone in the audience "was injecting other people with drugs."

On his Instagram account, Travis Scott sent in his condolences, saying he was devastated by the fatalities at the Houston Astroworld show.

Friends and loved ones mourned the victims at the concert venue, at a makeshift memorial of flowers and candles.

Houston officials did not immediately release the victims' names or the cause of death. Twenty-five people were taken to hospitals by ambulance on Friday, with 13 still hospitalized on Sunday, five under the age of 18.