Migrants walk in a caravan bound for the United States, in Tapachula, state of Chiapas, southern Mexico, on Sept. 4, 2021. Migrant caravans traveling from Central America to the Mexican border with the United States became frequent since 2018. Photo: Xinhua

Tens of thousands of migrants are in a situation of "extreme vulnerability" in Mexico due to overcrowding, inadequate healthcare and the risk of coronavirus infection, Doctors Without Borders (MSF) said Monday.

The medical aid group blamed the plight of migrants in two border cities in southern and northern Mexico on the "failure" of asylum policies and continuous deportations from the US. 

MSF has deployed an emergency team to provide medical, psychological and social assistance in Tapachula, where around 40,000 migrants are stuck, it said.

"These people find themselves with few options for shelter, crowded together or on the streets with poor sanitary conditions and risk of contagion by COVID-19," said MSF's Christoph Jankhofer. "We are concerned about the symptoms of anxiety, depression and hopelessness that the population presents due to the lack of response from the authorities," he added.

Over the past week Mexican security forces have broken up several migrant caravans heading north from Tapachula towards the US, prompting accusations of excessive use of force.

Mexican authorities last week suspended two immigration agents accused of beating a migrant.

Mexico has seen increased arrivals of migrants heading north to flee poverty, violence and other problems following US President Joe Biden's arrival in the White House with a promise of a more humane approach.

In northeastern city of Reynosa, on the border with the US, around 2,000 mostly Central American migrants are living in tents, MSF said.

They are exposed to searing temperatures, serious security threats and inadequate access to basic services, the group warned.

Mexican President Andres Manuel Lopez Obrador said last week that he would write to Biden to insist on the need to tackle the causes of migration because simply detaining people was not the answer.