Mexican authorities have said that they have no evidence of the disappearances [Reuters]

An armed gang has kidnapped 50 Central American migrants who were travelling on a cargo train in southern Mexico.

The abductions on the night of December 16 came after the group of men held up the train, struck and robbed passengers, El Salvador's foreign ministry said on Tuesday.

Women and children were among those kidnapped, according to a priest who runs a local shelter for migrants.

The captured passengers have not been seen since the incident.

"Witnesses said that the subjects climbed up on the wagons, struck the migrants with machetes and took their belongings," El Salvador's foreign ministry said in a statement.

"Afterwards they took away all the women traveling on the train."

Mexico's interior ministry said that it had found no evidence of the disappearances.

Priest Alejandro Solalinde said 17 people, who had also been travelling on the northbound train, arrived at his shelter on December 17 and said the migrants were abducted in Chahuites, about 300 km from the border with Guatemala.

Solalinde, who runs the Hermanos en el Camino (Brothers on the Way) shelter in the town of Ixtepec in the southern state of Oaxaca, said that he believes that the Zetas drug gang was behind the abductions.

"Fourteen witnesses stayed in the shelter, and yesterday and the day before someone came to ask that they be handed over to the Zetas," Solalinde said.

The witnesses were subsequently taken to a safe location by authorities, he said.

Members of the Zetas group are believed to have kidnapped and killed 72 migrants at a ranch near the US border in August.