A 13-year-old Connecticut boy was in grave condition Thursday after apparently overdosing on the opioid fentanyl while in school, Hartford Mayor Luke Bronin said.

Two other seventh-graders from the Sports and Medical Science Academy in Hartford also were sent to Connecticut Children’s Medical Center for observation after being exposed to the drug, but it was unclear late Thursday if they had ingested it, Bronin said.

“It appears that the drug was brought to the school by a student,” Bronin said. “There were multiple additional bags of what we believe was fentanyl found around the school, which again we believe was brought by a student.”

The 13-year-old collapsed at about 10:30 a.m. inside a gymnasium at the school, which is a public college-preparatory middle and high school with a focus on sport and medical sciences. After a school nurse began CPR, emergency officials arrived and took over the care, restoring the student's heart rhythm, authorities said.

Authorities said staffers identified two other possible victims, who never lost consciousness and were in a classroom in a different part of the building.

“I don't think it's clear where it was ingested,” Hartford Police Chief Jason Thody said. “It seems as though (the three boys) were together when it was ingested and then separated.”

The school was evacuated and drug-sniffing dogs were brought in to help with a thorough search of the building.

Thody said that because some forms of fentanyl can be dangerous when airborne, those who were evacuated from the school had to be decontaminated with a cleaning solution that dissolves and neutralizes the drug before being allowed to leave.

Leslie Torres-Rodriguez is the Superintendent of Hartford Public Schools, said the schools are not supplied with Narcan, the emergency drug used to treat opioid overdoses.

Hartford police were investigating to determine the source of the drugs.

No charges had been filed as of Thursday evening.