Law enforcement agencies in northern India have rescued at least 160 Nepalis trafficked across the border since two powerful earthquakes struck last year, a senior Indian official said.

The twin quakes in April and May killed more than 8,800 people and injured tens of thousands in the impoverished Himalayan nation. Around two million were left homeless.

Following aid agency warnings that human traffickers could prey on vulnerable survivors in the aftermath of disasters, authorities in Uttar Pradesh passed an order directing areas bordering Nepal to be vigilant.

"The day the earthquake happened, I went to my office and issued a sensitisation letter to all the district magistrates and superintendents of police in all the seven districts which border Nepal," Kamal Saksena, home secretary for Uttar Pradesh state, told the Thomson Reuters Foundation.

"Then we conducted video conferences with all of them and asked people from all the relevant ministries such as women and child and labour and other departments to all attend so that there was communication and coordination."

Trafficking was rife in Nepal even before the earthquakes, with an estimated 12,000 Nepalese children trafficked to India every year, according to a 2001 International Labour Organisation study.

Activists said risks were much higher after the quakes when traffickers or "brokers" duped devastated families who had lost their homes and breadwinners to hand over their children with the promise of a monthly salary and a good job in India.

Yet the reality is very different. Girls and women not recruited into prostitution are sold as domestic slaves in India and other countries. Boys are taken into forced labour.

Saksena said authorities provided training for more than 4,000 people, including police inspector generals, district magistrates, railway police, border forces, child protection officers and shelter home staff.

This included examining suspected trafficking routes and destination points such as train stations, border check posts and interstate bus stations.

They also focused on how to identify suspected traffickers and the proper procedures after rescues and arrests.

"We tell them what to be alert for. People travelling with large numbers of children for example," Saksena said in an interview on Saturday on the sidelines of an anti-human trafficking conference in the eastern town of Siliguri.

"One sub-inspector intercepted a couple in their mid forties who had 15 children. The children lied saying their parents were taking them to Mumbai for sight-seeing. We found out the children were sold to the traffickers for 1,500 rupees ($22) each."

Saksena said between 50 to 60 arrests have been made so far and the cases are currently being investigated. Most of those rescued since April have been repatriated, he added.

"Prior to earthquake, we weren't really doing that much training," he said, adding that had now changed. "To coordinate with all the stakeholders with the same sensitivity and synergy is quite an effort."