Villahermosa - An infamous cargo train ridden by Central American migrants heading to the US derailed in a remote region of southern Mexico on Sunday, killing at least five and injuring at least 35, authorities said.
The toll was expected to rise. Hundreds of migrants sometimes ride the roof of the cargo train known as "The Beast", braving brutal conditions for a chance at crossing into the US.
The Red Cross said an undetermined number of people were trapped.
Tabasco state Civil Protection chief Cesar Burelo Burelo said the accident took place at 03:00 on Sunday in an area surrounded by lakes and forest that is out of cellphone range.
Burelo said eight cars had derailed and authorities didn't yet know why.
The Tabasco state government said at least 250 Honduran migrants were on the train heading north from the Guatemala border.
The federal government said 16 of the 35 injured in Sunday's accident were gravely hurt. Fifteen of the badly injured have been moved to the nearest hospital in the state of Veracruz, which borders Tabasco.
The Red Cross said dozens of soldiers, marines and civilian emergency workers were trying to get access to the area, which ambulances couldn't reach. Officials were trying to establish air or water links to the scene.
Mario Bustillos Borge, the Red Cross chief in Tabasco, described the rescue as "a complex situation" that was making it difficult to get rapid confirmation of the true number of dead and injured.
"There are some very high estimates, and others that are more conservative," he told a local radio station, without providing details.
While the number of Mexicans heading to the US has dropped dramatically, there has been a surge of Central American migrants making the journey, fuelled in large part by the rising violence brought to their homelands by the spread of Mexican drug cartels.
Other factors, experts say, are an easing in migration enforcement by Mexican authorities and a false perception that Mexican criminal gangs are not preying on migrants as much as they had been.
Central American migration remains small compared to the numbers of Mexicans still headed north, but steeply rising numbers speak starkly to the violence and poverty at home.
About 56 637 non-Mexican migrants, most of them Central Americans, were detained by the US Border Patrol along the border with Mexico between October and May last year.
That's more than double the 27 561 detained in the same period a year earlier. Meanwhile, the number of Mexican migrants caught at the US southern border decreased 7% last fiscal year, to 188 467.