Police in India's flood-hit north said Thursday they had stepped up operations and made several arrests to prevent an increase in child trafficking in the devastated region.

The country's worst floods in decades have displaced nearly three million people and triggered mass migration from Bihar, which is among India's poorest states and a source of cheap migrant labour — including children.

Activists say the floods and migration have made children vulnerable to trafficking.

"We have received a few complaints. Some people have been arrested," Yashwant Malhotra, police chief of the local anti-human trafficking body, told AFP by phone.

Extra police had been deployed at railway stations to look out for suspected traffickers, he said.

A children's rights group said that since the floods it had rescued more than 30 children who had been bought from parents to be taken to work in roadside eateries and factories across the country.

"Parents are given up to 1,000 rupees (21 dollars) for a child and are told they will be sent monthly wages for the work done by the child," said Bhuwan Ribhu of Save the Childhood Foundation.

"That money is never sent and children normally work 12 hours a day for less than a dollar a week," Ribhu said.