A school trip for a group of Nanuet seventh-graders took a harrowing turn after their charter bus caught fire on I-684 in Harrison Thursday.

Forty students and five teacher chaperones from the Nanuet Middle School were on their way to Boston when a parent chaperone following the bus in a car spotted smoke pouring out of the bus' engine. The bus driver pulled over near Exit 2 in Harrison and all the students escaped unharmed before the bus became engulfed in flames.

"The bus was half in flames when we got there," says Trooper Joe Izzo, of the New York State Police. "Then it spread to the rest of the bus. Responding fire crews were able to put it out without incident."

State police officials in Somers say the fire was caused by a mechanical failure.

The students and teachers from Nanuet M.S. were picked up by another charter bus and were taken to Boston. The principal of the school says the students did not miss any of the events planned for their tour.