At least 25 children died and dozens needed hospital treatment after apparently being poisoned by a school meal, sparking violent protests and angry allegations of blame.
The children aged four to 12 fell ill on Tuesday after consuming a lunch of rice, soybean and lentils in the impoverished state of Bihar.
The school, at Mashrakh village in the district of Chapra, provided free meals under the Mid-Day Meal Scheme, the world's largest school feeding programme involving 120 million children.
Medical teams treating the children said they suspected the food had been contaminated with insecticide.
"It appears to be a case of poisoning but we will have to wait for forensic reports ... Had it been a case of (natural) food poisoning, so many children would not have died," Poonam Kumari, local government administrator at the village, told Reuters by phone from Mashrakh.
"The administration has helped cremate 21 children and, unfortunately, four more children have to be cremated," she said, adding that the remainder of a total of 48 children who consumed the contaminated food were being treated in Patna.
"We feel that some kind of insecticide was either accidentally or intentionally mixed in the food, but that will be clear through investigations," said R.K. Singh, medical superintendent at the children's hospital in the state capital Patna.
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"We prepared antidotes and treated the children for organophosphorous poisoning," he said.
Organophosphorus compounds are used as pesticides.
The state government said it was investigating the cause of the disaster.
The school headmistress fled after the deaths became known and was dismissed, P.K. Shahi, Bihar's education minister, told a news conference.
"In spite of the cook's complaint (over the smell of cooking oil used for the food), the headmistress insisted on its use and the cook made the food. The children had also complained about the food to the cook," Shahi said.
The cook, who also fell ill after eating the food and was hospitalized, told Reuters television it had looked as if there was a layer of residue at the bottom of the oil jar.
"I thought that this is locally-made oil as often there is an accumulation of residual waste at the bottom ... generally we get just about enough oil to prepare one meal, as there is no space for storage," Manju Devi said in Hindi.
Opposition parties accused the Janata Dal party-led government of acting too slowly to hospitalize the children and dozens of people took to the streets to protest, television channels showed.
Demonstrators pelted a police station with stones, set ablaze buses and other vehicles, chanted slogans denouncing the state government and burned effigies of Bihar Chief Minister Nitish Kumar.
"I feel that the government completely failed vis-a-vis the evacuation of the affected children," said Rajiv Pratap Rudy, a spokesman for the main federal opposition Bharatiya Janata Party, said.
"As soon as my boy returned from school, we rushed to the hospital with him," said Raja Yadav, the father of one schoolboy. "He was vomiting and he said his stomach was aching."
Three of the children being treated in the hospital were in critical condition, doctors and Shahi said.
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Kumar has ordered an inquiry into the incident and has offered 200,000 rupees to the families of those who have died, state food minister Shyam Rajak said.
Bihar, bordering Nepal, is one of the most impoverished states in India, according to government data.
Kumar came to power in 2005, ousting a government which had been blamed for rampant corruption and sluggish growth in the poor eastern state.