Central Americans cling to the back of a truck as a thousands-strong migrant caravan slowly heads north in hopes of reaching the U.S. border, between Pijijiapan and Tonala, Chiapas state, Mexico, before dawn on Friday, Oct. 26, 2018. (AP Photo/Rebecca Blackwell)

Pijijiapan - Thousands of Central American migrants were Friday crossing southern Mexico, where they approached the boundary between the states of Chiapas and Oaxaca on their way to the United States.

The caravan, whose number of participants Mexico puts at about 3 600 and organizers at 5 500, reached Tonala at more than 250 kilometres from Mexico's border with Guatemala on Friday.

Some travelled on to Arriaga near the border of Oaxaca, where the entire caravan was due to arrive by the evening.

The caravan left Honduras on October 13 and crossed the Guatemalan-Mexican border last weekend.

The migrants, whom US President Donald Trump has vowed to turn back from the US border, still have thousands of kilometres to go.

Some are trekking on foot, while others travel on lorries or other vehicles.

"I hope God helps to open [Trump's] heart so he lets us through," Junior Anel Lopez from Honduras said in the town of Pijijiapan, from where the caravan pursued its route to Tonala.

The migrants met with an outpouring of solidarity from Mexicans along their route. "As a mother and wife, I feel I need to help," said Rubicelia Santiago Ovanolo, who was offering the migrants coffee in front of a church in Pijijiapan.

A musical group also came to entertain the migrants on a square. Dancing relieved foot pain, said Carlos Adalso, 27, who explained he had left El Salvador because gays were persecuted there.

Another migrant, Jose Alcantara, said he had had enough of Honduras after he only received two months' wages for eight months of work.