Nearly two dozen people were treated for burns on their feet after walking on hot coals during a motivational seminar conducted by self-help expert Tony Robbins in San Jose, California, local media reported.

Firefighters treated at least 21 people for burns to the soles of their feet, several of them second- and third-degree, on Thursday night, according to a report in the San Jose Mercury News. At least three people went to the hospital, although none of the injuries was life-threatening, the report added.

It was the first night of the motivational seminar called “Unleash the Power Within,” a four-day Robbins event attended by some 6,000 people, the Mercury News reported.

Close to midnight after the main part of the event, participants walked to a park where 12 lanes of hot coals measuring 10 feet by two-and-a-half feet lay on the grass, the newspaper reported.

“I heard wails of pain, screams of agony,” one of the attendees, Jonathan Correll, 25, told the Mercury News.

Full story: Those burned in Tony Robbins hot coal walk were warned of danger – NBC News