The Mexican government had said that the US expelled more than 2.8 million migrants at its border crossings in over three years under Title 42, a Covid-related restriction set to expire on Thursday.
Of the 2, 825, 970 people expelled, the vast majority were deported at the US-Mexico border (2, 710, 494), with six out of 10 being Mexican nationals (1, 641, 746), Xinhua news agency quoted the Interior Ministry as saying in a statement.
The bulk of the remaining migrants deported at the southern border came from countries including Guatemala, Honduras, El Salvador and Nicaragua.
First implemented in 2020 under former President Donald Trump's administration, Title 42 allows US authorities to swiftly expel would-be migrants attempting to cross the border from Mexico -- including those seeking humanitarian asylum -- using the Covid-19 pandemic as justification.
But with the policy due to expire a minute before midnight on Thursday, officials fear border authorities may be overwhelmed by an influx of migrants even as record numbers in recent years have already strained resources and left border towns scrambling for solutions.
While the US claimed the measure aimed to protect against the spread of the virus, the Ministry noted in its statement that it may have aggravated the outbreak by having "exposed thousands of migrants to greater risk" through mass deportations.
In light of this, Mexico's Ministry of Foreign Affairs said it would reinforce its consular assistance and protection in the US to safeguard the rights of Mexican citizens.
One of the worst-hit cities in the US to be affected by the end of Title 42 is El Paso, Texas.
Migrants, many of them confused about the impending rule changes, have been left sleeping rough in makeshift campsites on city streets over the last several days.
Several thousand were camped out earlier this week around a single church in the city centre, reports the BBC.
"We've never seen this before, " Mayor Oscar Leeser said on Wednesday. "Something has to change. As a community, we can't do this forever."
Leeser warned that across from El Paso alone, an estimated 10, 000 migrants were "lined up at the border, waiting to come in".
In a bid to stop the flow, the Biden administration introduced strict new rules for asylum seekers on Wednesday, including barring those who cross illegally from applying from asylum for five years.
US officials have also announced new changes aimed at encouraging migrants to seek legal pathways to the country, as well as strict penalties and swift deportation for those who cross illegally.