Dakar - Over 50 schoolgirls have succumbed to what educators here are calling "collective hysteria" - fainting and screaming, requiring hospitalisation.

The girls' bizarre behaviour caused firefighters to shut down the secondary school where the incident occurred. All of the 53 girls and two boys that experienced the unexplained fit were evacuated to the capital's main hospital.

"The phenomenon started in one of the classrooms of the Class 5 girls," said Adina Aidara, the principal of Lamine Gueye School in Dakar where the strange event occurred. "Three students, all girls, fell down. The same phenomenon was repeated 30 minutes later during recess - this time involving high schoolers. We called the fire department to evacuate the victims," he said. The incident began on Friday at 9 am. By 1 pm (local time), the school had sent 55 students to the hospital in ambulances, he said.

"It's an event that is completely out of the ordinary," said Aidara. At the city's central hospital, anguished parents fussed over their daughters. A 15-year-old girl, who spoke with her mother that her side, said she was in the middle of chatting with a friend. "Suddenly I had a horrible headache. It hurt so much that I started screaming. And then I fainted. From that moment on, I no longer knew where I was," she said.