Around 300 students were taken ill on Tuesday after inhaling toxic gas emitted by a sugar mill near their school in Shamli district, the police said.
Uttar Pradesh Chief Minister Yogi Adityanath has ordered a probe into the matter.
The students of a private school in Shamli started complaining of stomach ache, nausea and burning sensation in their eyes after gas leakage from a neighbouring sugar mill.
Those who fell ill were rushed to the district hospital. A dozen students, who were in serious condition, have been referred to Muzaffarnagar and Meerut hospitals.
Panic-stricken parents rushed to the school and took their wards away. Total chaos prevailed in the school for over two hours as medical teams rushed to the school late and the children were left to fend for themselves, some parents said.
Senior district officials including the District Magistrate and the Superintendent of Police (SP) rushed to the school as news of the incident spread.
"We have come to know that similar incidents had taken place in the past. A probe is on and strict action will be taken against those responsible," ADG, Meerut zone, Prashant Kumar said.
He said all the children are safe and are undergoing treatment in various hospitals.
Principal secretary, Information, Awanish Awasthi told PTI that "The CM has ordered a probe into the Shamli incident by Commissioner of Shaharanpur and directed the DM and all local officers to provide all possible help to the affected children."
Locals alleged that sugar mill employees used to discharge chemicals in waste dumps leading to emission of harmful gas inhaling which children took ill, with some of them falling unconscious.
Local residents and parents also accused the district administration of turning a blind eye to their demands in the past against the sugar mills which frequently release chemical gas that pose serious health hazard to the children and others in the vicinity.
The owner of the sugar mill was absconding, the police said.
