Chinese authorities say a man has injured 20 children, three of them seriously, in an apparent knife attack on a primary school classroom in Beijing, Independent reported.

A male suspect was arrested at the scene and an investigation into what happened has begun, according to the government of Xicheng, a major district of the capital.

All the children were taken to hospital and the three who were badly injured were in a stable condition.

The local authorities would not comment on whether a weapon was used in the attack, but posts on social media said some of the children suffered knife wounds to the head.