(The Blaze/AP) — Fire officials in California say at least 21 people were treated for burns after attendees of an event for motivational speaker Tony Robbins tried to walk on hot coals.

The San Jose Mercury News reports that at least three people went to a hospital and most suffered second- or third-degree burns.

Robbins was hosting a 4-day gathering called “Unleash the Power Within” at the San Jose Convention Center. Witnesses say on Thursday, a crowd went to a park where 12 lanes of hot coals were on the grass.

At Least 21 Treated For Burns After Attempting Fire Walking at Tony Robbins Event

Tony Robbins (Photo by Frederick M. Brown/Getty Images)

Robbins’ website promotes “The Firewalk Experience” in which people walk on super-heated coals.

Witness Jonathan Correll says he heard “screams of agony.” He explained it was hard to watch as one young woman appeared to be in so much pain.

“I heard wails of pain, screams of agony,” he said. “It was horrific.”

Correll continued: “It was people seriously hurting, like they were being tortured… First one person, then a couple minutes later another one, and there was just a line of people walking on that fire. It was just bizarre, man.”

Henry Guasch, 19, said that after walking across the hot coals while chanting his mantra, “cool moss,” he felt powerful.

“Overcoming something like that, it’s a breakthrough,” he said, explaining that he slowed his pace at one point and got a minor burn.

Another fire walker, Andrew Brenner said the keys to making it across the coals without getting burned are faith and deep concentration.

“I did it before, didn’t get into the right state and got burned,” said Brenner. “I knew I wasn’t at my peak state. I didn’t take it as serious.”

Fire Capt. Reggie Williams says organizers had an open fire permit and emergency personnel were on standby.

“We discourage people from walking over hot coals,” Williams said.

CBS San Francisco has more:

Also, for your viewing pleasure, a previous Tony Robbins fire walk can be viewed here: