Millions of Indian children are getting deworming treatment in a massive national campaign to prevent parasitic worms from infecting them and impairing their mental and physical development.

In a village on the outskirts of the Indian capital, the children washed their hands and lined up to chew the deworming tablets given to them by their teachers and health workers before opening their bags for studies on Wednesday morning.

The campaign is targeting 270 million children across the country for Wednesday's effort and another next week for children missed the first time, the Health Ministry said in a statement.

Worms interfere with nutrient uptake in children and could lead to anemia, malnourishment and physical and mental impairment.

The World Health Organization estimates that 220 million children between the ages of 1 and 14 are at risk of parasitic worm infection in India.

On Wednesday, nearly 900,000 teachers, principals and health workers were mobilized in schools and government-sponsored child and mother care centers.

Priya Jha, who leads non-governmental organization Evidence Action's work in India, said details of a second dose to the children would be decided soon by the Indian government on the basis of a study carried out in different states.

She said the campaign went off smoothly with children and their parents eager to participate in it. The tablets were provided by the WHO and the Indian government.

Parasitic worm infections are mainly caused by lack of proper toilets, unclean drinking water, poor hygiene and dirty surroundings in Indian villages and towns.