A bus crash in the Mexican state of Oaxaca killed 18 people on Friday, according to local authorities, who say most of the passengers were migrants.

Three children and two women are among the victims, all of whom are from Venezuela and Haiti, the Oaxaca state attorney general said. At least 27 people were injured and transported to nearby hospitals.

Pictures posted by authorities on Facebook show the large bus flipped over and heavily damaged on a curve of the mountainous Oaxaca-Cuacnopalan highway.

Authorities are investigating the cause of the accident, which took place at 5 a.m. local time (7 a.m. ET).

The tragedy follows the deaths of at least 10 Cuban migrants, including a child, on Sunday, when the truck they were traveling in also overturned in southern Mexico, according to local authorities.

Venezuela and Haiti are sources of large numbers of migrants traveling northward, fleeing insecurity and economic crisis at home.

US and Mexican officials have struggled to respond to the arrivals, with Washington putting increasing pressure on Mexico City to shoulder more responsibility for people crossing its territory.

Food shortages and limited access to health care have driven more than 7.7 million people from Venezuela alone -- a scale of displacement that outpaces Ukraine, where there's an active war.

On Thursday, senior officials in the Biden administration said the US would restart deporting Venezuelans directly to Venezuela in an attempt to curb the record influx, marking a major shift in policy.

Haiti meanwhile is waiting for a new multinational mission to help bring order to the country, currently roiled by unchecked gang violence, kidnappings and food insecurity.