Twelve migrants, including two who were dead, were found inside a locked train car 20 miles east of Uvalde, Texas on Friday, authorities said.

Five of the 10 survivors were transported to San Antonio hospitals, according to the mayor of Uvalde.

Some needed to be airlifted, and others were treated at the scene.

The discovery was made by Border Patrol agents on railroad tracks parallel to Highway 90 at about 1:30 pm, Uvalde Police Chief Daniel Rodriguez told KENS 5 News. 

Uvalde Mayor Don McLaughlin told Texas Public Radio on Friday that the train had been sitting on the track for about three hours – where temperatures reached 87 degrees Friday – before the migrants were found. 

“911 got a call – don’t know if it was from a family member or one of the migrants who were locked in the shipping container,” McLaughlin told the outlet.

Immigration and Customs Enforcement’s Homeland Security Investigations unit said it was investigating the possibility of a human smuggling operation, according to Texas Public Radio.