SAN JOSE — Amid inspirational talk, chanted mantras and shouts of victory at a late-night firewalking event attended by thousands on Thursday, came agonized shrieks from followers whose soles were scorched by the superheated coals, witnesses said.

At least 21 people were treated for burn injuries after taking part in the crowning event of the first day of a Tony Robbins function downtown, including at least three who went to the hospital, a San Jose fire captain said.

The people who suffered various second- and third-degree burn injuries were among more than 6,000 who attended the motivational speaker’s event at the San Jose Convention Center called “Unleash the Power Within.”

After the event, which ended about 11 p.m., the crowd walked across the street to the park where 12 lanes of hot coals measuring 10 feet long and 2 1/2 feet wide rested on the grass.

Jonathan Correll, 25, decided to check out what was going on when “I heard wails of pain, screams of agony.” He said one young woman appeared to be in so much pain “it was horrific.”

“It was people seriously hurting, like they were being tortured,” he said. “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.”

Correll, a San Jose City College student, said he saw between 10 and 15 people being treated. He said he videotaped the scene for about 5 minutes before an event staffer told him to put the camera away.

But on a break from day two of the four-day event Friday night, others who walked on the coals said it was nothing short of life-changing.

Henry Guasch, 19, of Mountain View, said that after crossing the coals while chanting his mantra of “Cool moss,” he felt powerful.

“Overcoming something like that, it’s a breakthrough,” he said, adding that he did slow his pace in the middle of the field and got a minor burn.

Guasch and Andrew Brenner, another fire walker, both said that the keys to not getting singed are faith and concentration.

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

He said his feet blistered after the walk about eight months ago at another Robbins event, but he didn’t need medical attention.

Kim, a 22-year-old who didn’t want her last name used because she is still attending the event, said her two friends who did the walk seemed fine at first, but their feet started to blister about 10 minutes later. She said other people had similar problems, a number of whom were soaking their feet in a fountain at the park.

“It seemed abnormal that so many got hurt,” she said, adding that many attendees on Friday complained about blisters and a woman sitting near her had both feet completely bandaged.

David Willey, a physics instructor at the University of Pittsburgh at Johnstown in Pennsylvania, has published a text and video on the physics of firewalking and stated that it “does not need a particular state of mind.”

“Rather, it is the short time of contact and the low thermal capacity and conductivity of the coals that is important,” he wrote. He added that ash that builds up on coals can provide further insulation.

It took about 90 minutes for everyone to walk across the coals, fire officials said. It is not known how many of the people who attended the conference took part in the firewalk.

San Jose fire Capt. Reggie Williams said event organizers had emergency personnel on standby and had obtained an open fire permit from the San Jose Fire Department, Williams said. A fire inspector from the department was at the event to make sure there was no accidental fire.

A statement released Friday from Robbins Research International, said, “We have been safely providing this experience for more than three decades, and always under the supervision of medical personnel … We continue to work with local fire and emergency personnel to ensure this event is always done in the safest way possible.”

On the Tony Robbins website, he promotes “The Firewalk Experience,” a process where people walk across coals between 1,200 and 2,000 degrees Fahrenheit.

But that’s not something the San Jose Fire Department recommends, Williams said,

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

Contact Eric Kurhi at 408-920-5869. Contact Mark Gomez at 408-920-5869.