The 23 children who died after eating a free school lunch in India were poisoned by a pesticide.

The poisoning is believed to have been caused by an organophosphate-based pesticide mixed in with the food, Bloomberg reported.

Police collected samples from the school meal and sent them to a forensics lab for testing, the results aren't back yet but medical examiners are almost sure the mass death is linked with the chemical.

"It seems organophosphorus was mixed in the food. The quantity was huge, which is why we've seen such devastating effects," Amarkant Jha Amar, medical superintendent at the Patna Medical College and Hospital where the children and school cook were treated, said.

About 60 children ate the meal of "rice, lentils, soybeans and potatoes," which had been cooked in an outdoor oven.

The meal's ingredients were reported to have had a strange smell and color during preparation.The principal was warned the food should not be served to the children, but the suggestion was ignored.

Aditya Prasad is one of the survivors of the incident. He remembers seeing his friend throw up and collapse, his sister also vomited. As a reaction Aditya stopped eating, which most likely saved his life.

"These kids were being fed sub-standard food. We all know that as fact in this village," Dilip Kumar, 20, a local resident, said.

The principal, Meena Devi, is on the run from police.

Nineteen of the 23 children who died have been buried "in and around" the school yard, some only feet away from where they consumed the deadly meal, the BBC reported.

Children in nearby areas have been refusing to eat their midday meals.

India's central government started a scheme to get more kids in school by providing free meals, but they have often been accused of bad hygiene, Bloomberg reported.

Investigations found 563 metric tons of food rotted before even reaching its designated schools. Since the program started not one meal has been examined by a medical officer.

The report said the food should be taste-tested by at least two adults before it is served to the school children, and must be totally free of insecticides.