Two migrants were found dead and at least 10 were hospitalized Friday after police in South Texas received a call that they were “suffocating” in a freight train traveling near the US-Mexico border.

The Uvalde Police Department said Border Patrol was informed of the phone call and able to stop the train. About 15 migrants were found inside, according to a statement from the department.

Union Pacific railroad said in a statement that the people were found in two cars on the train traveling east from Eagle Pass bound for San Antonio: 12 in a shipping container and three in a hopper car. The two people who died were in the shipping container, The Associated Press quoted the statement as saying.

At least four people were air-lifted to San Antonio, authorities said, while others were taken to local hospitals.

The condition of all of those hospitalized was not immediately known. University Health in San Antonio tweeted that it had received two male patients, one in critical condition and one in serious condition.

Uvalde Police Chief Daniel Rodriguez told the San Antonio-Express News that dispatchers received a 911 call about 3:50 p.m. from an unknown person seeking help. The train was stopped near the town of Knippa, which is less than 100 miles (161 kilometers) from the southern border.

“We’re still trying to determine if it was from someone inside the car,” Rodriguez said. “We’re assuming it was from inside one of the cars.”