GANDAMAN, India (AFP) - A children's playing field outside an Indian primary school was turned into a mass graveyard on Thursday as victims of a poisoned lunch scandal that killed 23 youngsters were laid to rest.

As grieving parents spoke of how they relied on the school to give their children their main daily meal, officials in impoverished Bihar state tried to stem a wave of panic among other pupils who were dumping their free lunches.

The police meanwhile stepped up their investigation, exploring the possibility that the food given to the youngsters was poisoned deliberately, as the school's headmistress remained on the run.

The burials were held on an area of open ground just outside the school where pupils play during their breaks, according to an AFP correspondent at the scene.

"The school killed our children and so we decided to bury all of them here," said Ms Shanti Devi, whose daughter was among those being laid to rest outside the school in Gandaman village.

"The government is responsible for converting a playground into a burial ground," she told AFP.

The sense of anger was echoed by many other parents as they tried to come to terms with the deaths of loved ones.

Some 30 children are still being treated for food poisoning, although doctors say their condition is not life-threatening.