NEW DELHI - At least 20 people have been injured in a gas balloon blast in the central government-controlled territory of Chandigarh in northern India, police said Monday.

"The blast took place at an annual function of a private academic institute in Sector 34 late Sunday evening when some former students were releasing gas balloons as part of celebrations," a senior police official said.

The nitrogen gas balloons caused an explosion after getting stuck in a bulb that triggered an instant heat, he said.

All the injured students have been admitted to a nearby government hospital, where some are said to be in critical condition.

A probe has been ordered into the incident, he said.

"We are probing if the academic institute secured permission from the local police station for holding the function and action will be taken against the owner if found guilty of negligence and not adhering to basic safety norms," the official added.