•The group walked over a bed of coals that was several metres long and felt pain shortly after.
•Often known as fire-walking, it is sometimes used in motivational courses and charity events.
Twenty-five people have been treated for burns in northern Switzerland after they walked across hot coals as part of a team-building exercise.
Thirteen of them were taken to hospital and treated for more severe injuries after the incident on Tuesday evening.
A large emergency response, including 10 ambulances, arrived at the private event at around 18:00 (16:00 GMT).
The group walked over a bed of coals that was several metres long and felt pain shortly after, police said.
It is not yet clear if there was an issue with the set-up of the coals or with how the group walked across them.
Officials have opened an investigation and taken evidence from the site, which is in the Au peninsular just south of the city of Zurich.
Walking across a bed of hot coals, often known as fire-walking, is sometimes used in motivational courses and charity events.
It involves walking barefoot over a bed of hot embers or coals. It is also used in many parts of the world as a rite of passage or test.