Police in Mexico's southern Chiapas state have found 513 migrants inside two trailers bound for the United States.
Chiapas state police discovered the migrants on Tuesday while using X-ray equipment on the vehicles at a checkpoint in the outskirts of city of Tuxtla Gutierrez, the National Immigration Institute said in a statement.
Police have also arrested four people accused of smuggling the migrants, who are from Central and South America and Asia, Chiapas state prosecutors said in a statement.
The alleged smugglers tried to escape police but were chased down and captured, prosecutors said.
The immigration institute said 410 of the migrants were from Guatemala, 47 from El Salvador, 32 from Ecuador, 12 from India, six from Nepal, three from China and one each from Japan, the Dominican Republic and Honduras.
There were 32 women and four children among them.
The migrants told authorities they had agreed to pay $7000 to be taken to the US, the immigration institute said.
Hundreds of thousands of migrants travel through Mexico each year in the hopes of reaching the US, but this was the largest group rescued in recent years.
In January, Chiapas state authorities discovered 219 migrants squeezed into a trailer. Most of those migrants were from Central America but six were from Sri Lanka and four from Nepal.