The protesters left a small space to consume liquids and used alcohol to wipe away drops of blood from the stitches, as Mexico's migration agency called the measures "worrying".
A dozen undocumented migrants on Mexico's southern border have sewed their mouths shut in a bid to convince the country's immigration authority to grant them passage toward the US border.
The migrants, mostly Central and South Americans, helped each other seal their lips using needles and plastic threads on Tuesday.
They left a small space to consume liquids and used alcohol to wipe away drops of blood from the stitches, Reuters images show.
"The migrants are sewing their lips together as a sign of protest," said Irineo Mujica, an activist at the demonstration.
"We hope that the National Migration Institute can see that they are bleeding, that they are human beings."
Mexico's migration agency (INM) said in a public statement that "it is worrying that these measures have been carried out with the consent and support of those who call themselves their representatives, with the intention of pressuring authorities on an attention already provided".
'We are like prisoners'
Some were carrying their children when they staged the dramatic protest in Tapachula, a border city with Guatemala.
For months, the city has been filled with thousands of migrants waiting for papers to be able to freely cross the country.
"I'm doing it for my daughter," said Yorgelis Rivera, a Venezuelan. "She has not eaten anything in the last few hours and I see no solution... from the authorities."
"We are like prisoners here," Rivera said, adding that she has been waiting for a response from Mexico's migration agency for more than a month.
The agency said it continues to attend cases, adding that priority has been given to vulnerable groups, such as children, adolescents, pregnant women, victims of crime, people with disabilities and the elderly.
The institution said it receives more than a hundred applicants at their offices in the southern city every day.
In recent years, the number of migrants arriving in Mexico fleeing violence and poverty has jumped.
In 2021, Mexico recorded an 87 percent increase in the number of asylum applications, mainly from Haitians and Hondurans.
The United Nations refugee agency (UNHCR) recently said Mexico should consider new aid programmes amid a surge in the arrival of foreigners, many of them Venezuelans, for whom Mexico now requires a visa.