At least five people were killed when a cargo train nicknamed "La Bestia," or "The Beast," on which would-be migrants hitch rides toward the U.S. border, derailed in a remote area of southern Mexico on Sunday, emergency services said.
Some local media said the death toll could be as high as 50, and said ambulances were unable to reach the scene of the accident in Huimanguillo in the southern state of Tabasco because of the difficult terrain.
Images from the scene showed freight cars upturned and wheels separated from their base. Officials said eight of the 12 cars overturned, and that a Honduran man was among the dead.
"This train carries a lot of (illegal) migrants from Central America," Cesar Burelo, emergency services director in Tabasco, told local television. "(Those five) were the visible dead," he added. "It could be that as the structure of the train is removed ... more bodies could appear."
He added it would be difficult to determine the total number of people who were aboard at the time of the pre-dawn accident.
"It's very likely that (surviving travelers) have left the scene."
Luis Felipe Puente, national emergency service coordinator, said on Twitter that 35 people were injured, 16 seriously, but the death toll could rise.
Sixteen of the wounded had been transported to local hospitals, Burelo said.
Migrants often jump aboard La Bestia under cover of darkness. At times, several hundred migrants have been found on the train, either in freight cars or sitting on top.
In a press release, the foreign ministry lamented the accident and said it was helping Central American embassies whose citizens were affected by the crash.