Thousands of women and children affected by Nepal's devastating earthquake are now at risk from sex traffickers, aid workers have warned.

Sex trafficking is already a significant problem in Nepal – the UN estimates that between 12,000 and 15,000 girls are trafficked every year. Many are taken across the porous border with India, where they are forced to work as sex slaves in brothels.

The 7.8-magnitude earthquake on April 25 killed more than 8,000 people, left almost 18,000 injured, and aid agencies have struggled to reach remote communities. With infrastructure and livelihoods destroyed, the current situation makes it easier for traffickers to prey on women and children.

"Our teams on the ground in Bhaktapur, Gorkha and the surrounding areas of Kathmandu have seen people going there in the name of relief and promising jobs to children and adolescent girls," Bhuwan Ribhu from Indian child protection charity Bachpan Bachao Andolan told Sky News. "And we fear they will be trafficked for sexual exploitation and for forced labour."

A senior aid official told the Guardian: "There is nothing like an emergency when there is chaos for opportunities to ... traffic more women. There is a great chance that everything that is bad happening in Nepal could scale up."

Local health worker Rashmita Shashtra also told the Guardian: "People here are now desperate and will take any chance. There are spotters in the villages who convince family members and local brokers who do the deal. We know who they are."

According to the Times, Nepali authorities stopped a group who had picked up 40 children from a remote area hit by the earthquake and were taking them to the capital, Kathmandu, where there are a number of bars and massage parlours which also function as brothels.

Indian armed forces rescued four children from traffickers in Raxaul, an Indian-Nepalese border town, last Monday. Since then, SB Sharma, director general of the Indian Armed Border Force, told reporters that they have stepped up security in the town.