The Fire Service has put out a fire at Hutt Valley High School which started this morning.
A stand-alone classroom at the Woburn Road school was ablaze when crew arrived about 11am.
The Fire Service said it received calls at 10.40am and four crews from Lower Hutt went to the school.
Two Wellington City fire crews were also deployed.
The large school in Lower Hutt has more than 1600 pupils and about 100 teachers.
A standalone classroom at Hutt Valley High School was engulfed in flames when crews arrived.
Senior station officer Rob Sullivan said no students were in the classroom at the time, and all students were safely evacuated to a nearby sports field.
The fire was put out shortly before midday.
He said it was too early to say what caused the fire, but a fire investigator had already started his investigation.
"The fire has destroyed about half the building. The building was used as a cooking building for the students here," he said.
"It's about 20 metres by 10 metres."
Students were told the school would be closed for the rest of the day.
One student, Daniel Hall, 15, said he noticed the smoke as he was evacuated from his classroom near the blaze.
"We saw smoke rising and it escalated to big grey clouds, and it just got bigger and bigger and it looked like a big bomb was dropped.
"It was hard to believe because you get fire drills and false alarms and that, but this time it was actually a real fire."