India's human rights body is investigating reports that more than 100 children fell ill from eating a school lunch after a dead snake was found in the food.

The cook reportedly still served the lunch despite removing the dead animal from it, the National Human Rights Commission (NHRC) said in a statement.

The commission said about 500 children are believed to have been served the meal in the city of Mokama in Bihar state, eastern India.

After children started falling sick, locals blocked a road in protest, the NHRC said.

"The commission has observed that the contents, if true, raise a serious issue of violation of the human rights of the students," it said.

The statement demanded a "detailed report" within two weeks from senior state officials which will include "the health status of the children".

The free school meals, know as the Mid-Day Meal, were first introduced for children from poor backgrounds in the southern city of Chennai (Madras) in 1925.

One of the biggest such schemes in the world, it was introduced to combat hunger and boost school attendance. However, there have been complaints of poor food hygiene.

In 2013, tainted food was blamed for the deaths of 23 schoolchildren in Bihar state.

Police said "very toxic" levels of a pesticide had been detected by scientific tests.