A knife-wielding assailant injured 14 children at a kindergarten in the western Chinese city of Chongqing on Friday morning, police reported. The attacker, a 39-year-old woman, was taken in custody and no motive for the assault was immediately publicized.

The report posted on the police force's microblog said the attack at the Xinshiji Kindergarten in the city's outskirts took place at 9:30 a.m. as the children were returning to classes.

It said all were receiving treatment in hospital. A doctor who answered the phone at the city's Banan People's Hospital confirmed the children were there but declined to give any details or his name, referring questions to the local government.

No other information about the attacker was given, other than her surname, Liu. Footage posted on social media showed injured children walking to ambulances from the school gate, with some being placed on gurneys.

China has suffered a number of such incidents in recent years, blamed largely on the mentally ill or people bearing grudges.

In June, a man used a kitchen knife to attack three boys and a mother near a school in Shanghai on Thursday, killing two of the children. Police said the assailant was unemployed and carried out the attack "to take revenge on society."

Chinese law restricts the sale and possession of firearms, and mass attacks are generally carried out with knives or homemade explosives.

Almost 20 children were killed in school attacks in 2010, prompting a response from top government officials and leading many schools to add gates and security guards.