Hasselt Mayor Hilde Claes said Friday that two more people had died, bringing the toll from Thursday night's disaster to five. All the dead were Belgians.
Organizers of the annual Pukkelpop festival say tents collapsed, and people were scrambling to find shelter. Extra buses and trains were called into service to get the 60,000 festival goers home.
Skin, the lead singer of Skunk Anansie, which was performing on the main stage when the storm hit, described the chaos on the band's Facebook page. She said "a burning hot sunny day turned into a mini-hurricane."
"(A) tower fell onto our truck, we had to run for our lives mid-set as hail hit the stage and the wind began to tear it to pieces," she wrote. "This was the scariest moment I have ever seen or felt in my 20 years of being an artist."
Dr. Pascal Vranckx of Jessa Hospital in Hasselt said many of the injured were hit on the head by flying or falling debris.
At a news conference Friday, Hasselt officials and festival organizers described weather conditions at the event's opening day as exceptional and said weather forecasters had not predicted a storm of that intensity.
The Belgian weather service refused to give the exact speed of the wind, saying only that the storm was "violent."
The three-day festival's lineup featured internationally known acts, including Foo Fighters, Eminem and The Offspring.
The Associated Press contributed to this report.