Burnt soles rather than cleansed souls awaited attendees at motivational speaker Tony Robbins's latest life coaching seminar, with 21 people needing treatment after a painful walk across coals.

During a four-day gathering in California entitled Unleash the Power Within, the famed lifestyle guru encouraged participants to take a leap of faith and test their luck on the red-hot surface.

Emergency services were called to deal with the fall-out, as many in the group suffered second- and third-degree burns. Three needed hospital treatment, the San Jose Mercury News reported.

"I heard wails of pain, screams of agony" one witness told the newspaper.

"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," Jonathan Correll, 25, said.

The injured fire walkers were among thousands who attended the Robbins event. As part of the multi-day seminar, a crowd were led to a park where 12 lanes of hot coals had been laid out.

A brochure for the Unleash the Power Within event suggests that once you overcome the fear of walking on coals of between "1,200 and 2,000 degrees Fahrenheit" you can "conquer the other fires of your life with ease".

A spokesman for the San Jose fire department told the San Jose Mercury News that it does not recommend that people undertake the endeavour.

Robbins has used fire-walking throughout his career as a motivational speaker and life coach.

In a statement, the Robbins Research International told the newspaper: "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."