SAN ANTONIO – Forty-six people were found dead in a tractor-trailer on the Southwest Side, and 16 have been transported to area hospitals, according to San Antonio police and fire officials.

“It’s tragic,” Nirenberg said. “They had families… and were likely trying to find a better life. It’s nothing short of a horrific, human tragedy.”

Authorities could not immediately confirm if the victims were migrants or what country they were from.

San Antonio Police Chief William McManus said officers received a call 10 minutes before 6 p.m. Monday to the 9600 block of Quintana Road when a person working nearby heard a cry for help.

When the worker approached, he saw several bodies inside an 18-wheeler trailer with its doors partially open.

Crews with San Antonio Fire Department arrived at the scene to find “stacks of bodies” in the trailer and many people too weak to let themselves out, according to SAFD Chief Charles Hood.

Hood said 46 people, men and women who ranged from teens to young adults, were pronounced dead at the scene.

He said they died from heat stroke and heat exhaustion as the trailer had no air conditioning and no water. Temperatures reached more than 100 degrees on Monday.

First responders helped 16 people — 12 adults and four minors — out of the trailer.

The survivors were rushed to local hospitals with heat-related injuries, Hood said.

“Very hopeful they’re going to survive,” he said.

Ten medic units were used to transport the survivors. Hood said 60 members of the SAFD will undergo behavioral assessments after seeing the stacks of bodies. Overall, he said the response “went very smoothly and very quickly.”

McManus said three people are in custody. However, he said he was unsure if they were connected to the tragedy.

McManus said federal Homeland Security Investigations would be taking over the investigation.

Antonio Fernandez, CEO of Catholic Charities, said they are working to help survivors.

He said the Archbishop is devastated after hearing the news.

KSAT meteorologists said the high temperature reached 101 degrees before going down at 2 p.m. on Monday once the rain arrived.

KSAT will update this story with the latest information as it becomes available.