A secondary school maths teacher sprayed herself with a flammable liquid and set herself alight in a school yard in southern France at break time, France's education minister said.
The motive behind the incident, in the Mediterranean city of Beziers, was not immediately clear.
The teacher, whose name has not been released, was flown by helicopter to a hospital in nearby Montpellier suffering from serious burns.
"I saw a person who was running and on fire, it was a human torch," said Dolores Roques, a fellow teacher at the school, on France-Info radio.
"I didn't believe my eyes. It seemed unreal. The students were screaming everywhere."
Education Minister Luc Chatel visited the hospital, and said a psychological support unit would be set up in the school.
Mr Chatel said the woman's health "is extremely worrying".
Speaking on RTL radio, he described her as a "teacher who is in a situation of great fragility" who has been undergoing medical and professional help and that an investigation would help determine the reasons for her "desperate act".