Bilaspur: A Class IV girl student was injured in a mysterious explosion in the washroom of a private school in Chhattisgarh's Bilaspur city on Friday, a police official said.

The explosion, the nature of which is not clear at present, took place at 10:15am in the school situated in Mangla area, Civil Lines City Superintendent of Police (CSP) Nimitesh Singh said.

"On the sound of the blast, teachers who were busy with final exams underway, rushed into the washroom and found the girl lying on the floor injured. She has been hospitalised. The school management suspects someone placed placed sodium or other chemicals used in the laboratory to cause the blast," Singh said.

A forensic team has launched its investigation and school staffers and students are being questioned, the CSP informed.