The unused college building in Wainuiomata, near Lower Hutt city, has been severely damaged and part of it has collapsed because of the fire.
The fire broke out at the three-storey building at about 12.20am, Wellington fire service shift manager David Meikle told NZPA.
At the height of the blaze there were ten fire trucks at the college but there had been no reports of injuries, he said.
Firefighters are now standing down.
The cause of the fire was unknown and would be investigated today, Mr Meikle said.
