The fire broke out in unit 603 at 215 Wurtemburg St., a highrise apartment building near Rideau Street and the Rideau River, at about 2:15 a.m. Wednesday.
Ottawa police arrived first and started to alert people in the building to the fire and help them outside to wait in OC Transpo buses dispatched to the scene, paramedics said in a media release.
Heavy smoke conditions were reported on multiple floors inside the building, according to the fire department.
Crews had to use a ladder to get some people out of the building safely.
Nine people were treated by paramedics for smoke inhalation and taken to hospital. They were all in stable condition, paramedics said. Another four people were assessed at the scene but didn’t need to go to hospital.
The fire was knocked down by about 2:45 a.m., firefighters said.
A damage estimate was not immediately available and the cause of the fire is under investigation.