A man attacked a group of children with a hammer in front of a elementary school in Xicheng, a district of the Chinese capital.
More than 20 children are said to be injured, with three hospitalised in very serious conditions. All children are aged between three and ten years.
Local police said they arrested the attacker, but did not release any details about him.
Xicheng District announced that a full investigation would be carried out to understand the motivations for the gesture and examine security flaws that allowed him to act almost undisturbed.
The administrators of Beijing No.1 Affiliated Elementary School of Xuanwu Normal School, where the attack took place, did not make any statements but said they were ready to collaborate with the authorities.
The Global Times, an online newspaper close to the Communist Party, reported that the attack occurred at 11 am.
Violent crimes are quite rare in China, where the law imposes the death penalty on anyone who attacks Chinese and foreigners.
The attack comes a day after a Chinese man was put to death for injuring 12 children in a knife attack at a nursery in China