Three students were killed and two critically injured when the water tank of a private school in Arunachal Pradesh collapsed on Saturday morning.

Police have detained six persons associated with St Alphonsa School in Naharlagun for questioning. Naharlagun superintendent of police Mihin Gambo told The Telegraph that the incident occurred around 9.30am.

“The three deceased were Class IX students while the two injured were Class VI and Class VIII students. The injured are being treated at the Tomo Riba Institute of Health and Medical Sciences (TRIHMS),” he said.

The police said the investigation is under way to find the cause of the collapse of the rectangular water tank but “apparently” it may have been caused because of a “construction fault”.

The tank was “constructed above another structure” with one side of the tank wall giving way and its remains falling on the deceased students who were close to the tank.

“We will consult experts as to what might have led to the collapse. We have detained the owner of the school building, the principal and four wardens for questioning,” Gambo said.