Six tribal children died and more than 60 fell ill after drinking adulterated milk in a state school in eastern India, officials said Friday.

The students in Jharkhand state, aged between 8 and 13 years, began vomiting and complaining of stomach aches after drinking milk and eating snacks Thursday evening, officials said.

More than 30 children are in hospital in the state capital Ranchi, nine in critical condition, doctors said.

"Adulterated milk seems to have caused food poisoning," said Bandhu Tirkey, the state's Human Resources Development Minister, without elaborating further.

The school is run by the state's welfare department to give free education and food to children of ethnic tribespeople, among the poorest and least-developed communities in India.

The state government has suspended teachers from the school for dereliction of duty, because food and drink is prepared under their supervision, an official said.

Villagers gathered near the school Friday to protest against the deaths.

"We never imagined that free education and free food would cause the death of my son," the father of one of the children said.