The bulk of the migrant caravan travelling from Central America towards the US border are preparing to leave Mexico City to start the most dangerous part of their journey.

Almost 4,000 Central American migrants will depart a stadium in southern Mexico City having spent much of the week in the sports complex.

The group have spent the past few days in the Mexican capital resting, receiving medical attention and deciding how to proceed with their arduous trek.

Eddy Rivera, 37, from Honduras, said he had left behind four children and a wife and wanted to start the next phase of the journey.

"We are all sick, from the humidity and the cold," Mr Rivera said. "We have to get going; we have to get to Tijuana."

Though he was unsure how an unskilled farmworker like himself would be allowed into the US, he had a simple dream: earn enough money to build a little house for his family back in Puerto Cortes, Honduras.

Felix Rodriguez, 35, of Choluteca, Honduras had been at the Mexico City sports complex for more than a week.

"We all want to get moving," he said. But he was waiting for the main group to leave, noting it was "better to leave in a group, because leaving in small bunches is dangerous".

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The migrants' plan was to take a subway to the northern part of Mexico's capital, then proceed first to the city of Queretaro, followed by Guadalajara, Culiacan and Hermosillo until the migrants arrive in Tijuana on the US border, said Nashieli Ramirez, director of Mexico's Human Rights Commission.

Mr Ramirez said that 90 per cent of the at least 4,000 migrants remaining in Mexico City would depart before dawn on Saturday and that 400 had decided to stay in Mexico.

Queretaro Governor Francisco Dominguez said the migrants would stay at the Corregidora stadium in the state's capital and that authorities were ready to host 4,000 people.

For many, it will be the first time they have ever been in a metro system, and they have little knowledge of the city or the 1,740 mile route to Tijuana that lies ahead of them. Drug cartels and gangs operate in many parts of northern Mexico.