Thousands of migrants are marching through southern Mexico as part of a mass protest to demand the end of detention centres.
Last month, 40 people were killed when fire ripped through a facility in Ciudad Juárez, a city on the US border.
“The only thing we are asking for is justice, and to be treated like anyone else,” Salvadoran migrant Miriam Argueta told AP news agency.
They are hoping to reach the capital Mexico City in about 10 days.
The caravan of about 3,000 people started walking at dawn on Sunday from the Mexican city of Tapachula, near the Guatemalan border. On Sunday they slowly made their way through the rural state of Chiapas, walking in more than 35C (95F) heat.
They are mainly from Central America, Cuba, Venezuela, Ecuador and Colombia.
Demanding better treatment for migrants, some are carrying signs reading “government crime” and “the state killed them”, referring to those who died in the fire.
It is unclear how many of the protesters may continue on to the US border, as has happened in the past. Large groups have often been broken up by authorities well before they reach either Mexico City or the US-Mexico border.
The migrants travel in large groups for safety – they face several threats along the way, particularly from dangerous organised crime gangs and corrupt local law officials. Migrant rights groups say that breaking up the caravans has forced many people into the hands of people-smuggling gangs.
Mexico is struggling to deal with an influx of migrants who are fleeing instability, violence and poverty in their own countries.
While most are hoping to reach the US, some do apply for asylum in Mexico.
The immigration centre in Tapachula – the biggest in Mexico – is one of the main bottlenecks on their journeys. Nicknamed the “migrant prison”, refugee processing offices in the city are overwhelmed.
The fire on 27 March started when migrants set fire to foam mattresses “when they learned that they’d be deported”, Mexican President Andrés Manuel López Obrador said.
There were also reports that they were protesting over the poor conditions they were being held in.
There was outrage when video footage of the fire showed three uniformed officials walking out of the room, appearing to leave the migrants behind in a locked cell as the flames spread.
Five people are facing homicide charges, including a Venezuelan man believed to have started the fire, three immigration agents and a private security guard.
Meanwhile, on 11 May the Biden Administration expects to lift Title 42 – a controversial Trump-era policy brought in during the pandemic, which allows border agents to immediately deport undocumented immigrants.