Mexican police discovered Tuesday 513 undocumented migrants from Latin America and Asia traveling in subhuman conditions in two tractor-trailers, authorities in the southern border state of Chiapas said.

The migrants coming from China, India, Nepal, the Dominican Republic, Ecuador, Guatemala, Honduras and El Salvador are now in Tuxtla Gutierrez, the state capital, the Chiapas Attorney General's Office said in a communique.

Since the migrants' presence was detected Tuesday before dawn, authorities have provided them with food and medical attention along with judicial and psychological support, the AG's office said.

The two Mexican nationals who were driving the trucks are in custody.

Preliminary investigations indicate that each of the 513 migrants paid $7,000 to traffickers who promised to transport them across Mexico and smuggle them into the United States.

The presence of the illegal aliens was detected with the aid of X-ray equipment at a checkpoint in Tuxtla Gutierrez. The trucks failed to stop and were pursued until they were caught up with several kilometers (miles) down the road.

Official figures say that every year some 300,000 undocumented migrants, mostly from Central America, cross the somewhat more than 1,000 kilometers (620 miles) of border that Mexico shares with Guatemala and Belize to try and reach the United States.

The most recent report on the matter from Mexico's independent National Human Rights Commission, or CNDH, found that at least 11,300 migrants were kidnapped on Mexican soil from April to September 2010.