Thirty-three children were injured after a helium gas cylinder exploded inside the Vivekananda Vidya Niketan School campus in Ambikapur city in the district, police said.

"The incident took place after 2.15 pm on the school grounds during school lunch hours when three people who were using helium cylinders to fill air balloons got injured after the cylinder and the balloon burst," Superintendent of Police Sunil Sharma said on Thursday.