The 22 children, from the Dandaman school in Saran district, Bihar died after eating the meal of daal, rice, potato and soya beans. A further 24 children and the school's cook remain in hospital. It appears the oil used to cook the soya was contaminated with a massive amount of agricultural pesticide.

"The incident smacks of a political conspiracy. The police may get vital leads once the principal is arrested," Bihar's education minister PK Shahi said.

School principal Meena Devi fled as soon as the children became ill, and police have begun a search for her.

It is alleged the principal bought the food for the midday meals from a shop owned by her husband Arjun Rai. The food was stored at their home.

"Arjun Rai, the husband of the school headmistress, had supplied the food material, he is an active member of a party and cousin of a local leader," Mr Shahi said, referring to the opposition Rashtriya Janta Dal party.

There is, as yet, no evidence the principal or her husband, or the opposition, deliberately plotted to poison children.

But Bihar's school tragedy has been debased by petty political squabbling. The government alleges a conspiracy designed to humiliate it, and party leaders on both sides have taken turns accusing each other of "insensitivity" and "leaving people to their fate".

The people, villagers in Dandaman say, have been forgotten.

The school's cook, Manju Devi, lost three of her own children, and eight from her extended family, to the contaminated meal.

Ms Devi ate the food too, and is currently in hospital in Patna.

"I used mustard oil in the cooking, about 250mg in quantity. I did not find anything wrong with the food when I ate it, but I doubted the oil," she told reporters from her hospital bed.

The midday meal is one of the world's largest free food programs, and feeds some 120 million school-aged children a day. First introduced in southern India, it has been replicated across the country as an incentive for poor families to send their children to school, and is aimed at combatting malnutrition, which affects more than 40 per cent of Indian children.

The food is typically vegetarian, and of local style, and while there are occasional complaints about its quality, this is the first large-scale tragedy.

The poisoned children died in agony.

The school had 150 children enrolled, but only 60 plates, so the midday meal was served in three groups.

Some of the first group started complaining of nausea and light-headedness within 15 minutes and other children were stopped from eating.

As more children fell violently ill, they were rushed to hospitals at Masrakh, about eight kilometres away.

"As long as villagers' children study in this school, they will be reminded of whom they lost because of government negligence," nearby resident Vinay Singh told reporters.

"I saw them gasping for breath. I saw them dying in the absence of doctors."

Already, 21 of the dead children have been buried in the schoolyard, less than 100 metres from the building, as a reminder to the government of its failure to protect its most vulnerable, villagers said.

In Chhapra, rioters torched four police and government cars, while women's groups in Patna attacked the state offices of the midday meal program.