The explosion took place in a dormitory at China's northwest Lanzhou University in Lanzhou, capital of Gansu Province, causing extensive damage to three floors of the six-floor building.
So far 28 out of the total 31 injured are still hospitalised, state-run Xinhua news agency said, adding that 24 of injured are students.
An initial probe suggests that the blast was caused by gas leakage from damaged pipes in a building that was adjacent to the dormitory and was being demolished when the workers accidentally cracked the pipes.
After smelling the gas leaking personnel did not take any measures in the following 17 hours, eventually causing the blast, the report said, adding the people responsible for the explosion are under police control.