Fans began climbing over metal barricades outside the entrance to the event minutes before the gates were scheduled to open at midday.
Three people incurred minor leg injuries after being trampled on and were transported to hospitals, according to KTRK-TV.
Rapper Scott posted an Instagram video of the stampede, showing people knocking down the barriers and running towards the festival entrance.
More than 50,000 people were expected to attend.
The line-up for the one-day festival included performances by Scott, Pharrell, Gucci Mane, and Rosalia, among others.
Houston Police reportedly announced in a since-deleted Tweet that they would be sending additional officers to the festival, adding that the event was understaffed and “promoters did not plan sufficiently for the large crowds”.