The youngsters, ages 11 to 13, were giving the free performance at St. Paul’s Church in Cambridge on Tuesday night when one of them suddenly became sickened by a smell and had trouble breathing, authorities said.

By the time first responders arrived at the church, multiple other kids were also experiencing similar symptoms.

“This was somewhat unusual,” the city’s fire Chief Thomas Cahill told WCVB at the scene.

“It was a routine medical call that quickly escalated into transporting eight children to the hospital. Not common.”

Photos from the scene showed fire crews carrying some of the kids away from the church.

A hazmat crew carried out a subsequent sweep of the building but no out-of-the-ordinary readings or smells were detected.

“At this time we are not sure of what caused the reaction,” Cahill said, adding that the building was quickly ventilated.

Roughly 70 others who attended the concert reported no symptoms, authorities said.

The children, who are members of the Chœur d’Enfants d’Île-de-France choir from Paris, are currently doing a tour of the US.

“Founded in 1970, the youth choir has travelled extensively and performed with some of the world’s top conductors and soloist,” the church said in a social media post advertising the concert.

“The concert will feature and exciting mix of sacred and secular repertoire, as well as popular French songs.”