Initial reports said multiple people had been injured in the derelict Amora Hotel, but the incident happened next door at Pringle House in Wakefield St.
The injured person waited hours for help but was alive and able to speak, Fire and Emergency assistant commander Martin Wilby said.
Firefighters were planning a floor-by-floor sweep of the building to see if there was anyone else inside, once it was deemed safe to enter.
A number of police cars, ambulances and fire vehicles were parked outside.
The company that owned the building said it had been under control of its insurance company.
Jason Dunn from Prime Property said the empty building was sealed off with security fencing, and internal access has been partially blocked.
There had been issues with people breaking into the building a number of times and fires being lit on the top floor.
"They were cutting through all of the steel, all of the ply shutters to actually access that. So we pulled all of that down, sealed the building off, put security fencing against all of the inner walls so that if they broke into the carpark building, they couldn't get in."
Dunn said he had been through the building with five different police squads in the last three months to stop people from entering.
Wellington Free Ambulance said it transported one patient in a moderate condition to Wellington Hospital.
