At least 54 persons, including 51 children, sustained burn injuries after a disgruntled man broke into a kindergarten and sprayed a corrosive chemical on students in southwest China's Yunnan province, authorities said on Tuesday, in one of the deadliest attacks on schools in the country.

The incident took place on Monday in the city of Kaiyuan, when the 23-year-old man, surnamed Kong, climbed into the kindergarten and sprayed caustic soda (sodium hydroxide), state-run Xinhua news agency quoted authorities of the city.

Fifty-one children and three teachers sustained burn injuries and were sent to the Kaiyuan People's Hospital and the PLA 926 Hospital for treatment, Hong Kong-based South China Morning Post quoted the Kaiyuan municipal government as saying.

The condition of two children was stated to be serious, the report said.

At about 3.35 pm (local time) the man climbed into the Dongcheng Kindergarten and sprayed sodium hydroxide on the children, it said.

He was detained about 40 minutes after the attack, police said.

Initial inquiries indicated that the man was acting out of 'revenge at society', but the investigation was continuing, the report said.

Sodium hydroxide, also known as caustic soda, has a highly caustic base and alkali that decomposes proteins at ordinary ambient temperatures and may cause severe chemical burns. It is highly soluble in water, and readily absorbs moisture and carbon dioxide from the air.

Attacks by, what police generally label as, 'disgruntled' people in China targeting civilians, especially kindergarteners, in public places to vent their anger have become common in recent years.

This attack was the worst in recent years as most of the attacks in the past were carried out using knives.

In September, eight students of a primary school in China's Enshi city were killed and two others injured in a brutal knife attack carried out by an ex-convict. The attack took place on Chaoyangpo grade school in Baiyangping, Enshi, Hubei province.

In May, 13 people were injured, two of them critically when a car driven by a disgruntled man ploughed through pedestrians in the southern Chinese city of Guangzhou.