Tuxtla Gutiérrez (Mexico) (AFP) - Mexican authorities have launched operations to block Central American migrants from illegally heading to the United States, stopping them from hitching rides on a freight train known as "The Beast."

The operations came after officials pledged to take action to stem a wave of unaccompanied child migrants who have flooded into the United States in record numbers in recent months.

Migrant rights activists and a consular official from a Central American nation said Mexican federal police and immigration agents conducted patrols late Thursday along the train tracks in the southern state of Chiapas, which borders Guatemala.

The train through Mexico is used by migrants who pay smugglers for the dangerous ride. It has been the scene of robberies and falls leading to severe injuries.

The authorities also launched raids in bus stations in the town of Tapachula, said Ramon Verdugo, who heads the local migrant shelter known as "Everything for Them."

Several migrants hid in surrounding bushes during the operations, Verdugo told AFP.

A consular official from a Central American country, who requested anonymity, said around 150 people were detained by agents who raided small hotels and restaurants frequented by undocumented migrants. They face deportation.

"They are grabbing them everywhere," including roads, said Carlos Bartolo Solis, head of the "Merciful Lord" shelter. He said many of the detainees have been minors.

Spokespeople for the federal police and National Migration Institute said they had no information about the operations.

Mexico had announced in July measures to stop migrants from hopping on the train as well as a program to handle the surge of migrants, including minors.

The number of unaccompanied children illegally entering the United States at its southern border fell by half over the past two months, from 10,628 in June to 5,508 in July.

Between October and June, more than 57,000 unaccompanied children were detained at the US-Mexico border, about three-quarters of them minors fleeing poverty and gang violence in El Salvador, Guatemala and Honduras.