Updated

At least two migrants have died and 15 were in need of "immediate medial attention" after they were found "suffocating" in a train car near a small Texas town in Uvalde County Friday afternoon, authorities said. 

The Uvalde Police Department said it received a 911 call just before 4 p.m. from someone who said there were "numerous undocumented immigrants ‘suffocating’ inside a train car," adding that the U.S. Border Patrol was informed and was able to stop the train two to three miles east of Knippa, Texas. 

The incident is suspected to be related to human smuggling, sources said. 

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Aerial view of train cars near San Antonio where migrants were found suffocating

Law enforcement vehicles and officers photographed via helicopter investigating train cars where more than a dozen migrants were found "suffocating" near San Antonio, TX. (Credit: KENS 5 San Antonio) (KENS 5)

Five migrants were flown to San Antonio-area hospitals and five others were flown to local hospitals. There conditions are unknown, police said.  

Aerial view of police vehicles and officers investigating train cars with migrants

Law enforcement vehicles and officers photographed via helicopter investigating train cars where more than a dozen migrants were found "suffocating" near San Antonio, TX. (Credit: KENS 5 San Antonio) (KENS 5)

U.S. Highway 90 was temporarily closed but reopened before 7 p.m. 

Helicopter view of Texas officers investigating train where migrants found suffocating

The migrants were "suffocating" inside the train car, a 911 caller told police.  (KENS5)

Union Pacific Railroad put out a statement that said, "At about 4 p.m. CDT, Union Pacific was notified by the U.S. Border Patrol that they had received a call from a distressed individual inside a Union Pacific rail car. A train was stopped near Knippa, Texas, and 15 people were found in two different train cars. Twelve of the people were found in an intermodal container. Two of those individuals died, four were air-lifted to San Antonio and six were taken to local hospitals. Three other individuals were found in a hopper car. The Union Pacific train was eastbound from Eagle Pass, Texas, to San Antonio. Union Pacific is deeply saddened by this incident and the tragedies occurring at the border. We take the safety of all individuals seriously and work tirelessly with law enforcement partners to detect illegal items and people riding inside or on our rail cars. This incident is under investigation."

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Helicopter view of Texas officers investigating train where migrants found suffocating

Knippa, Texas, is in Uvalde County, not far from San Antonio.  (Google Maps)

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The incident comes less than a year after 53 migrants died after being found inside a tractor trailer in the searing summer heat outside of San Antonio.  

One survivor of the journey, a 20-year-old from Guatemala, told The Associated Press that smugglers had covered the trailer’s floor with what she believes was powdered chicken bouillon, apparently to throw off any dogs at checkpoint.

The truck was carrying 73 people in all when it was found last June 27. Four people have been arrested in connection with the discovery of the truck, including the driver

The Associated Press contributed to this report.