Mexico border problems usually bring to mind President Trump's complaints about illegal immigrants. But Mexico also has trouble at its own southern border, where the government is trying to stem the tide of people entering the country. CGTN correspondent Franc Contreras went there to get a look for himself.

At the Suchiate River, marking the border between Mexico and Guatemala, an untold number of undocumented migrants cross daily on their way north.

FRANC CONTRERAS CIUDAD HIDALGO, MEXICO "Another group of immigrants arriving from Central America into Mexico; they are mostly from Honduras, the vast number of people fleeing Central America are coming from that country; they say they are fleeing violence."

Mexico's southern state of Chiapas shares a nearly 655-kilometer border with Guatemala. For decades, it has been the key crossing point for Central American migrants. In 2014 Mexico's federal government launched Operation Southern Border designed to crack down on illegal crossings. Apprehensions rose 85 percent during its first two years, according to the Washington Office on Latin America.

On a few occasions, undocumented immigrants trapped in trailers were rescued by authorities. Chiapas State has its own police force committed to protecting migrants. The director says his officers have dismantled 139 small-scale criminal organizations targeting undocumented immigrants crossing through Chiapas.

IGNACIO ALEJANDRO VILA CHAVEZ CHIAPAS STATE PROSECUTOR FOR CRIMES AGAINST IMMIGRANTS "Just a few days ago we rescued an under-aged minor who been kidnapped for two months by his own traffickers. We detained that migrant smuggler. That immigrant child was returned to his family and is now in their care."

CGTN cameras captured the moment one federal police agent and his unofficial helpers known as "madrinas" detained a van loaded with migrants on a highway near Tapachula. The men posing as police became visibly nervous and quickly left the area. A leading expert on Mexico's southern border says Mexican federal, state and local police are known to use men posing as police to extort undocumented immigrants.

ENRIQUE CORAZA DE LOS SANTOS COLLEGE OF THE SOUTHERN BORDER "The actions of public servants often do not measure up to what should be under the law, and there are many abuses against undocumented immigrants. Instead of helping, this sort of behavior increases the situation here of insecurity."

Corruption, limited resources and the ability of migrants and smugglers to evade detention only add to the complexity of this on-going drama. FC, CGTN, Ciudad Hidalgo, Mexico.