An infamous cargo train carrying at least 250 Central American migrants heading to the U.S. 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 as authorities moved heavy machinery to the scene of the derailment of the train known as "The Beast." Thousands of migrants ride its roof on their way north each year, braving brutal conditions for a chance at crossing into the U.S.

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 3 a.m. Sunday in an area surrounded by lakes and forest that is out of cell-phone 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 U.S. has dropped dramatically, there has been a surge of Central American migrants making the 1,000-mile northbound journey, fueled 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.

U.S. border agents caught 99,013 non-Mexican migrants, mostly from Central America, last fiscal year, nearly double the same period a year earlier and the highest since 2006. The number of migrants actually making the trip is believed to be far higher.