At least 1,300 migrants escaped from a detention centre in Mexico on Thursday night, highlighting how far a surge in arrivals has stretched the country's resources.
Roughly half of the migrants returned voluntarily to the Siglo XXI facility in the border city of Tapachula but around 600 people were still unaccounted for on Friday.
The incident arose when several inmates rioted at the centre in southern Mexico. Some threatened to set fire to the facility in protest at overcrowding.
The majority of migrants detained at Tapachula are Cuban but Mexican newspaper Reforma has reported Haitians and Central Americans were counted as among those who escaped.
"There was a large-scale unauthorized exit of people housed in the migratory station," the National Institute of Migration said in a statement.
Federal police with riot shields were sent to the compound but the institute said "there was no confrontation."
The escape occurred on the same day as Mexican human rights officials toured the centre to check conditions there.
It is the third time since October that migrants have rioted against conditions at the Tapachula centre. According to AFP, the facility was built to accommodate 900 people but residents say it sometimes holds up to 3,000.
Mexico has returned 15,000 migrants in the past 30 days, officials have said, amid pressure from President Donald Trump to block the flow of migrants heading north.
On Wednesday, the US president reiterated threats to send armed troops to the border if Mexico failed to deal with the so-called migrant caravan heading north.
Since October thousands of Cubans and Central Americans have travelled to Mexico in the hope of reaching the US.