Chennai: In a shocking incident, a ninth standard student on Thursday stabbed his teacher to death inside the classroom allegedly after he was repeatedly reprimanded by her over an issue.

The incident occurred at a private school here when science teacher Uma Maheshwari (39), who also taught Hindi, was taking lessons in class, police said.

The boy has been taken to custody but the exact motive behind the killing is yet to be ascertained, they said.

Meanwhile, school authorities described the incident as "unexpected," and indicated that the 15-year-old boy had come prepared with a plan.

"The incident happened at around 10.50 AM when he stabbed the teacher with a knife he had hidden in a book," Fr. Bosco Perianayagam, the Administrator of the school, said.

Other students raised an alarm before the boy fled the scene, he said. However, he was later taken into custody.

Uma Maheshwari is survived by two children, Fr. Bosco said, adding "We are in deep grief. This is an unexpected incident."