A fire alarm caused by smoke in the small gym ended classes 20 minutes early today at Palo Alto High School.

Principal Phil Winston said the source of the smoke was not immediately known to either him or the Palo Alto Fire Department.

Students evacuated to the football field after the alarm went off at 3:05 p.m. Fire trucks were on the scene within minutes. Students were released at 3:27 p.m. and did not return to seventh period classes, which end at 3:25 p.m.

More information to come.