Mexican authorities are working to identify 54 people killed when a speeding truck crammed full of migrants overturned in the southern state of Chiapas, a major transit point for those trying to reach the United States.
Bodies draped in white sheets lined the roadside, and travellers bleeding or with broken bones cried out in pain after the tragedy.
The crash is the latest incident involving poor people travelling through Mexico en route to what they hope will be a better life in the US.
Every year thousands of people attempt the long, dangerous journey, often seeking to escape violence and poverty they endure in their home nations, particularly in Central America.
"It hurts when these things happen," Mexican President Andres Manuel Lopez Obrador said, stressing that the way to tackle migration is to resolve the despair people feel at home.
"We have been insisting that one needs to address the root causes," he told a press conference.
Of more than 100 injured, 95 were from Guatemala, with the others from Honduras, Ecuador, the Dominican Republic and Mexico, officials said. Most of the dead were also from Guatemala.
It was unclear exactly how many people were travelling in the truck when it hit a wall near a police checkpoint and overturned.
"It was horrible to hear the wailing. I just thought about helping," said 18-year-old Sabina Lopez, who lives near the scene of the accident.
The driver, who fled the scene, appeared to have been speeding when he lost control on the highway connecting the town of Chiapa de Corzo with the state capital Tuxtla Gutierrez, officials said.
The National Institute of Migration said it was working to identify the dead, pay for funerals and help repatriate bodies.
It said survivors will be allowed to stay in Mexico.
At the roadside, AFP saw rows of bodies covered with white sheets as rescue workers, ambulances and police officials swarmed over the scene.
Ms Lopez, who lives in the El Refugio neighborhood nearby, told AFP she saw a man pleading with his wounded companion.
"Don't go to sleep, don't close your eyes," she recalled him saying. "Remember what you promised your mother! Hold on."
Another resident, Isaias Diaz, who arrived 15 minutes after the accident, described a ghastly scene, with "a lot of people lying around, some of them were already dead."
Mr Diaz said he saw "five, six children, injured obviously. People (who had) broken legs, ribs, heads, cuts on their necks, everything".
"The crying, the pain, the desperation. It was a very ugly atmosphere," he said.
Moving undocumented migrants hidden in trucks is the most common method used by human traffickers operating along the border from Guatemala into Mexico, where they then head north to the US border.
Others have opted to join the so-called caravans, in which people travel much of the long journey on foot, often battered by extreme weather in parts of Mexico -- not to mention the threat of extortion from drug cartels and other organised crime syndicates.
Migrants traveling north through Mexico in trucks often suffer accidents like this latest one.
Last month 12 migrants died when two trucks crashed and burned in Chiapas.
In a case that shocked a country sadly accustomed to violence, 16 Guatemalans and three Mexicans were found in January burned to death inside a truck with 113 bullet holes in the state of Tamaulipas which borders the US. Twelve members of an elite police unit were arrested.
In 2010, also in Tamaulipas, 72 migrants, most of them Central Americans, were shot dead by gunmen believed to be from Los Zetas, an ultra violent drug cartel.
The flow of undocumented migrants has grown since US President Joe Biden came to office with a promise to scrap the hardline border policies of his predecessor Donald Trump.
More than 190,000 migrants were detected by Mexican authorities between January and September, three times more than in 2020. Some 74,300 have been deported.
