Police in south Texas are investigating the death of a 3-month-old baby after they said his mother left him in a hot car Tuesday afternoon amid an unrelenting heat wave.

The fatality, which took place in Houston on a day when temperatures reached triple digits, marked the nation's 16th child reported to die so far this year in a hot vehicle.

Houston Police Department Assistant Chief Yasar Bashir said the baby's death took place after the child's mother and her two young children visited the Harris Center for Mental Health and Intellectual and Developmental Disabilities (IDD) in Houston, the public mental health outpatient authority for Texas' Harris County.

Police did not release the baby's name.

Hot car deaths:16 children have died in hot cars in 2023. Heat waves have made it more dangerous.

A baby dies in Houston after left behind in a hot car

Bashir said the family arrived at the facility "after 12 o'clock." The exact time remained under investigation on Wednesday.

The mother went into the building with her 4-year-old but left her 3-month-old alone in the car, Bashir said during a press conference Tuesday night.

When the mother and toddler returned to the car to leave about 3:25 p.m., she found her baby unresponsive inside. She then took the baby into the facility, Bashir said, and emergency responders were notified.

The baby was taken to a local hospital where he was pronounced dead.

Police: It's unclear whether the windows were rolled down

A preliminary investigation revealed the child was left unattended, Bashir said. The father was not at the scene.

As of Wednesday it was not yet clear whether the baby was left by mistake, police said.

Police were also investigating to determine whether the vehicle's windows were left down or if the car was left running with the air conditioner on.

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Baby's official cause of death pending autopsy

The medical examiner will conduct an autopsy to determine the child's official cause of death.

Bashir described the incident as tragic but avoidable.

"Houston gets very hot and under no circumstances you should leave a child in a car, not even for a moment," Bashir said. "Especially an infant or a child, the body temperature goes up very quickly."

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16 children succumb in hot car deaths this year

Prior to Tuesday, there had been 15 reported deaths of children left in cars in the U.S. in 2023, according to the National Safety Council, prior to Tuesday 15 child car deaths had been reported. Last year, 33 children died in the U.S. as a result of being left in a hot vehicle, according to the group.

On average, 38 children under the age of 15 die each year from heatstroke after being left in a vehicle, the NSC says. Nearly every state has experienced at least one death since 1998.

Natalie Neysa Alund covers breaking and trending news for USA TODAY. Reach her at [email protected] and follow her on X, the platform formerly known as Twitter @nataliealund.