BOSTON -- A small fire in a ceiling heating unit sent several Hopkinton elementary school staff to the hospital Friday morning complaining of dizziness and nausea.

The incident happened at about 8:30 a.m. at the Center School on Ash Street.

School officials said the motor of the school's ventilator overheated. It has been disconnected and removed.

The incident happened before the start of school, so there were no students inside, but some staff complained of an odor, dizziness and nausea.

Four staff were taken by Hopkinton ambulance to a local hospital to be treated for itchy eyes, dizziness and nausea. Four or five others were evaluated at the school but not taken to the hospital, the MetroWest Daily News reported.

Hopkinton's kindergarten and first graders attend the school. School was in session on Friday.