Fire officials said electrical contractors were working on the building when they noticed smoke and pulled the fire alarm, just before 8 a.m.
Firefighters arrived within minutes to find a fully involved fire in a unit on the 15th floor, said Fire Chief Matthew Pegg.
Fire investigators said the apartment was vacant and only the contents, such as clothing and furniture, inside the apartment were damaged.
Pegg said there were no injuries at the scene and the fire has been fully extinguished.
The apartment building is currently under construction after a massive blaze tore through the highrise in August 2018.
The fire destroyed electrical equipment throughout the building, causing around 1,500 residents to be displaced.
Residents have still not yet been allowed back into the building. Dates for returning have been pushed back multiple times, with the latest being this fall.
There is no word on the cause of the fire. Fire officials are still investigating.
WATCH: Videos from the 650 Parliament Street highrise fire that left many residents displaced