A 1-year-old boy died after he was left in a caregiver's truck for several hours, police in New Mexico said, calling it a "very tragic incident."

Police responded to a home in Albuquerque on Sunday after the child was found unresponsive in the caregiver's truck, according to Albuquerque Police Department spokesman Gilbert Gallegos.

The cause of death is pending an autopsy, though heat appears to have been a factor, Gallegos said. Police have not released the name of the child.

The child's parents had left the boy in the care of a male relative who lived at the home around mid-morning, Gallegos said. When family members contacted the relative later that day, the young adult realized the child was not inside, Gallegos said.

Family members attempted CPR until first responders arrived some time after 5 p.m., Gallegos said.

"They tried for a long time to revive the child. Unfortunately, the child died at the scene," Gallegos said during a press briefing on Monday.

Gallegos said he did not know the temperature inside the truck or exactly how long the child was left inside it, but that it was "several hours for certain."

No arrests have been made and the local district attorney's office is not filing charges at this time, Gallegos said.

Detectives interviewed the relative as well as a number of other family members and neighbors, Gallegos said.

The relative had left on foot before officers arrived at the scene, but returned to the home, Gallegos said.

"His relatives speculated that he was just traumatized," Gallegos said. "They said he was a good person but he was just in shock when this happened."

The incident remains under investigation.

Officers had contacted the New Mexico Children, Youth and Families Department and the department is not aware of any history involving the family, according to Gallegos.

"It's a really tragic incident, and our detectives are still investigating to try to get to the bottom of what happened," Gallegos said.

Prior to this incident, three children in the United States have died in hot cars so far this year, according to the national nonprofit Kids and Car Safety .

On average , nearly 40 children die in hot cars in the U.S. each year, according to the organization.