SAN MARTIN TEXMELUCAN, Mexico (Reuters) - Hundreds of migrants walking towards Mexico City on Thursday brought traffic to a halt at an important highway connecting the capital and the central state of Puebla, a Reuters witness and a local authority said.

       Migrants, many traveling with children, walked between autos and trucks and some even laid down to rest, a Reuters witness said. They had left the San Martin Texmelucan municipality in Puebla earlier on Thursday.

       "My son fainted, we don't have food, we don't have water," one mother, who declined to give her name, said in a video shared on social media. Other migrants were seen asking Mexico's National Guard security force for food, water or safe passage.

       Within recent days, dozens of migrants were sent from the poor southern border city Tapachula to Puebla as Mexican migration authorities attempted to dismantle an improvised camp and head off potential caravans of migrants walking north.

       It was not clear if the migrants trekking on the highway were part of the group that had been transported by migration officials.

       Under pressure to stem the number of migrants crossing the territory on their way north towards the border with the United States, the Mexican government has promised migrants humanitarian visas and transportation to other cities.

       (Reporting by Imelda Medina; Editing by Aurora Ellis)