TUXTLA GUTIERREZ, Mexico, Dec 10 (Reuters) - Most of the 55 people killed and the dozens who were injured when a truck packed with migrants flipped over in southern Mexico on Thursday were Guatemalans, authorities said on Friday, as survivors recounted the horror of the accident. People spilled from the truck carrying an estimated 166 travelers after it crashed on a curve outside the city of Tuxtla Gutierrez in the state of Chiapas, causing one of the worst death tolls of migrants in Mexico in the past decade. "We were traveling all squeezed together, there was no space, most of us were standing," Esvin Miguel Chipel, a 19-year-old Guatemalan survivor, said from the Tuxtla Gutierrez hospital where he was receiving treatment for his injuries. The government said state prosecutors had opened a murder investigation into the incident, which officials in Chiapas said had claimed the lives of 55 people, including a 16-year-old girl, and injured dozens more. The attorney general"s office said preliminary findings showed nearly all the victims were Guatemalans. Chiapas officials said three people from the Dominican Republic, a Honduran, a Mexican and an Ecuadorean were among the injured. Video footage showed bodies strewn on the ground after the overturned truck slammed to a halt by a highway footbridge. A few local residents reported seeing migrants fleeing the scene, while other survivors sat in stunned silence or struggled to get up. An unidentified Guatemalan man interviewed at the crash site said that when the truck driver tried to negotiate the bend, the weight of people inside caused the vehicle to flip. "The trailer couldn"t handle the weight of people," he said. In hospitals, doctors tended to shaken-up survivors of the crash who had broken bones, and suffered cuts and bruises. Emerson Morales, 23, from Guatemala"s Quiche region, sat slumped on a hospital cot at the Red Cross in Tuxtla Gutierrez with dark red scratches and bruising visible on his shoulder. He had also hurt his hip and neck and could not find the 17-year-old cousin he had set off with for the United States. "I feel bad," he said. "My main worry right now is for him." THE AMERICAN DREAM The head of Mexico"s National Guard, Luis Rodriguez, said at a government news conference that the driver of the truck fled the scene and that the migrants on board told authorities they had entered Chiapas a few days before the accident took place. Many stayed in the town of San Cristobal de las Casas in so-called safe houses run by people smugglers before boarding the truck on Thursday afternoon, Rodriguez said. The truck was due to take the migrants as far as the central city of Puebla before they moved on, the government said. Each month, thousands of migrants fleeing poverty and violence in Central America travel through Mexico to reach the U.S. border. They often cram inside large trucks organized by smugglers in dangerous conditions. Political leaders expressed consternation at the death toll, and urged migrants not to undertake the journey. "Human smugglers disregard human life for their own profit. Please don"t risk your lives to migrate irregularly," Ken Salazar, the U.S. ambassador to Mexico, said on Twitter. Many migrants fall prey to criminal gangs en route. In January, 19 people, mostly migrants, were massacred with suspected police involvement in northern Mexico. Record numbers of people have been arrested on the U.S.-Mexico border this year as migrants seek to capitalize on President Joe Biden"s pledge to pursue more humane immigration policies than his hardline predecessor, Donald Trump. Many survivors of the accident, including Ciriaco Rodriguez, a Guatemalan who fractured his arm, said they got into the trailer to make a new life for themselves in the United States. "More than anything it was to get to the American Dream," Rodriguez told Reuters.