The migrants had hopped on the train in southern Mexico and were traveling north through the Gulf Coast state of Veracruz when armed men demanding money attacked them with machetes and guns. Some jumped from the train to escape and others were thrown off, said migrant rights activist Tomas Gonzalez Castillo.
Gonzalez Castillo said he received reports of dozens of migrants seriously injured in the attack. Red Cross worker Daniel Fernandez said at least 200 migrants were treated for contusions and cuts at a migrant shelter in the town of Acayucan.
Veracruz's government, however, only confirmed that 10 people were injured in Wednesday's attack near the town of Cosoleacaque. It said nine of the injured had been treated at local hospitals and released, and that one remained hospitalized.
The government said the attackers were Hondurans already on board the train who tried to extort protection money from their fellow passengers.
"The injured, who are Honduran citizens, told immigration authorities that ... other migrants of the same nationality, who were also on the train, tried to charge them a fee and this led to a fight," it said.
Rev. David Hernandez Tovilla, who helps migrants in the Veracruz town of Coatzacoalcos, said witnesses told him the attackers were members of an organized crime group and that at least eight migrants were killed.
Veracruz Gov. Javier Duarte told reporters that no one died in the attack.
Jose Castro Marin, a 31-year-old migrant from Honduras, said the assailants were traveling among them.
He said that when the train started slowing down near Cosoleacaque at least 15 men pulled machetes and handguns and demanded $100 from each migrant if they wanted to continue on their journey.
"They started shooting at us and wounded one person on the leg," Castro said. "People started to run, some jumped off. I almost fell among the train's wheels."
Castro said at least 500 people were riding the train and that he's still looking for his brother who was traveling with him.
"My brother is missing," he said from a shelter in Acayucan. "People who saw him tell me the gunmen threw him off the train and that he hurt his head really badly. I don't know if they have him, if they kidnapped him."
Mexican drug gangs often recruit Central Americans to prey on their countrymen, who frequently have to pay off thieves, immigration officials, police and railroad employees as they head north on the sun-scorched trek. They also have to cross territory controlled by the Zetas gang, which has increasingly targeted migrants, kidnapping them for ransom or holding them for forced labor.