MEXICO CITY (AP) — Mexico is flying migrants south away from the US border and busing new arrivals away from its boundary with Guatemala to relieve pressure on its border cities.

In the week since Washington dropped pandemic-era restrictions on seeking asylum at its border, US authorities report a dramatic drop in illegal crossing attempts. In Mexico, officials are generally trying to keep migrants south away from that border, a strategy that could reduce crossing temporarily, but experts say is not sustainable.

The US Department of Homeland Security reported Friday that in the week since the policy change, Border Patrol averaged 4,000 encounters a day with people crossing between ports of entry. That was down dramatically from the more than 10,000 daily average immediately before.

Between the migrants who rushed to cross the border in the days before the US policy change and Mexico’s efforts to move others to the country’s interior, shelters in northern border cities currently find themselves below capacity.

In southern Mexico, however, shelters for migrants are full and the government is busing hundreds of migrants more than 200 miles north to relieve pressure in Tapachula near Guatemala. The government has also said it deployed hundreds of additional National Guard troops to the south last week.

Segismundo Doguín, Mexico’s top immigration official in the border state of Tamaulipas, across from Texas, said last week that the government would fly as many migrants away from border cities of Reynosa and Matamoros as necessary.

The transfers were “lateral movements to other parts of the country” where there were not so many migrants, Doguín said. He called them “voluntary humanitarian transfers.”

The Associated Press confirmed Mexican flights from Matamoros, Reynosa and Piedras Negras carrying migrants to the interior over the past week. A Mexican federal official, who was not authorised to speak publicly but agreed to discuss the matter if not quoted by name, said approximately 300 migrants were being transferred south each day.

Among them were at least some of the 1,100 migrants from Venezuela, Nicaragua, Haiti and Cuba that the US returned to Mexico in the week since the policy change.

“So the northern part of the migrant route is emptied out a bit, but the southern and middle parts remain extremely full and filling up all the time,” said Adam Isacson, director for defense oversight and a close observer of the border at WOLA, a Washington-based human rights organisation. “Obviously, that’s an equilibrium that can’t hold for very long.”

Mexico has moved migrants south in the past when there was concern about northern border cities’ capacity, but this time there are additional factors.

While the country’s shelters for migrants in the south are full, Mexico’s National Immigration Institute has closed its smaller migrant detention centers around the country and has undertaken a review of its large ones after 40 migrants died in a fire at a small detention facility in the border city of Ciudad Juarez in March.

The federal official said Mexico’s largest immigration detention centers are mostly empty. Two other federal officials, who also spoke on condition of anonymity, said Friday that “Siglo XXI,” Mexico’s largest detention centre, was empty.

Tonatiuh Guillén, former head of Mexico’s National Immigration Institute, said Mexico’s actions are contradictory — on one hand telling the United States it will contain migrants in the south, but on the other detaining fewer.

One morning this week, several hundred migrants waited on the outskirts of the southern city of Tapachula for government buses that would carry them to Tuxtla Gutierrez some 230 miles north.

Guillén said the document Mexico is issuing now to some migrants in Tuxtla Gutierrez — an expulsion order that gives migrants days or a couple of weeks to leave the country — does not give them other options, making it harder for them to seek international protection.