The youth suffered burns over 80 percent of his body in the self-immolation at Standley Lake High School in Westminster and was hospitalized in critical condition, the Denver Post reported.
Police said they do not know why the student, whose name was withheld, took the action, KMGH-TV, Denver, reported. The Post said as many as 70 students were in the cafeteria at the time.
A cafeteria worker who broke open a glass fire extinguisher case and doused the teen suffered a minor cut.
"I could see the kid in the flames," Kian Karp, 14, told the Post. "He was standing and it was almost like he was dancing around in the fire."
School district officials said the school would be closed for the rest of the day Monday as firefighters sought to ventilate the cafeteria and police scoured the rest of the campus to ensure no further danger. Police said they were looking into events that preceded the student's actions but do not think they received any threats of violence at the school.