Police are investigating after a boy suffered a medical emergency on a Fairfax County school bus Thursday afternoon and was later pronounced dead at a hospital.

First responders were called to 2300 block of Dulles Station Boulevard shortly before 2 p.m. for a report of a child experiencing a medical emergency, police said.

First responders performed lifesaving measures, but the boy was later pronounced dead, police said.

The boy was the only child on the bus at the time, police said.

Police said they did not have details about what caused the medical problem, the boy’s age, what school he attended or why he was the only child on the bus.

They referred questions to the Fairfax County Public Schools (FCPS), which released a general statement. John Torre, a schools spokesman, said a driver and an attendant were on the bus at the time of the incident. He declined to answer other questions, citing student privacy rules.

“The tragic death of an FCPS student today — apparently from a medical emergency that occurred on a school bus — is currently under investigation by Fairfax County Police,” Torre wrote in an email. “FCPS is fully cooperating with the investigation.”