TIJUANA, Mexico — American authorities suspended operations at the border crossing in San Diego on Sunday after hundreds of migrants tried to enter the United States.

U.S. Customs and Border Protection suspended all vehicles and pedestrians from passing through the San Ysidro Port of Entry at 11:30 a.m. after the migrants illegally tried to cross east and west of the inspection station. the agency said in a statement.

Some migrants said they tried crossing only after being denied access to a port of entry where they could claim asylum.

As of 2 p.m. local time, operations at San Ysidro had not yet resumed, the agency said.

The shutdown came after hundreds of migrants — many whom are fleeing violence in Central America — assembled Sunday morning on the Mexican side of the border. American military helicopters buzzed overhead as hundreds of Mexican federal police officers blocked the migrants from entering San Ysidro.

The migrants were part of a larger group of roughly 6,000 who’d crammed into several shelters in Tijuana — a situation the city’s mayor has called a “humanitarian crisis.”

In an interview Sunday, one of the migrants, Jorge Montoya, 43, described thousands of people staying in a rundown sports stadium with overflowing toilets. He and others called the conditions intolerable — but when Mexican authorities refused to grant them access to the port of entry, hundreds slogged across the sewage-laden Tijuana River in search of access to the United States.

 Among the throng were elderly people in wheelchairs and children with strollers. The group formed a human chain along the river’s steep embankments.

“We’re not running because we’re criminals,” Montoya said in an interview. “We’re running from the crime in our country.”

On the other side of the river, dozens of migrants broke through a wooden fence and climbed atop a freight train. Clutching Honduran and Guatemalan flags, they could see the United States from their perch — but there still appeared to be no way for them to cross.

The attempted crossing came after Trump administration officials and members of Mexico’s incoming government appeared to be at odds over a deal that could prevent asylum seekers from entering the United States.

Under the current system, asylum seekers can remain in the U.S. while their cases are processed in American courts. But the Trump administration wants them to remain in Mexico instead.

Two Trump administration officials told NBC News that the plan was a few weeks away from going into effect, though Jesus Ramirez Cuevas, a spokesman for recently elected Mexican President Andrés Manuel López Obrador, said no such agreement had been reached.