Mexico City authorities say that of the 4,841 registered migrants receiving shelter in a sports complex, 1,726 are under the age of 18, including 310 children under five.
"We need buses to continue travelling," said Milton Benitez, a caravan coordinator. Benitez noted that it would be colder in northern Mexico and it wasn't safe for the migrants to continue along highways, where drug cartels frequently operate.
He said the route and departure time would be decided at a meeting Thursday night.
The Mexican government has said most of the migrants have refused offers to stay in Mexico, and only a small number have agreed to return to their home countries. About 85 per cent of the migrants are from Honduras, while others are from the Central American countries of Guatemala, El Salvador and Nicaragua.
There have already been reports of migrants on the caravan going missing, though that is often because they hitch rides on trucks that turn off on different routes, leaving them lost.
However, the UN human rights agency said its office in Mexico had filed a report with prosecutors in the central state of Puebla about two buses that migrants boarded in the last leg of the trip to Mexico City early this week, and whose whereabouts are not known.
Mexico City is itself more than 600 miles from the nearest US border crossing at McAllen, Texas, and a previous caravan in the spring opted for a much longer route to Tijuana in the far northwest, across from San Diego. That caravan steadily dwindled to only about 200 people by the time it reached the border.
Fuentes warned the migrants that if they are separated from their children they should "say they want a lawyer and not sign any paper." Other activists and officials explained the options available to migrants in Mexico, which has offered them refuge, asylum or work visas.
The government said 2,697 temporary visas had been issued to individuals and families to cover them while they wait for the 45-day application process for a more permanent status.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)