A "carelessly discarded" cigarette is likely to blame for displacing 20 people and causing about $450,000 in damage after an early morning fire in the Centretown area, Ottawa Fire Services say.

Emergency crews say residents at 69 Raymond St., a row house, called firefighters at 5 a.m. to say they were evacuating their home. A second person also called 911 after they saw flames coming from the roof while passing the area on Highway 417.

Everyone made it out safely but the flames quickly burned through the roof, firefighters said.

Ottawa Fire crews operating at at 2-Alarm fire at 69 Raymond Street. Fire is in multi-door row. All occupants are safe. <a href="https://t.co/PthN0GlsQl">pic.twitter.com/PthN0GlsQl</a> —@OFSFirePhoto

4 children, 16 adults displaced

Crews had to open up neighbouring units to stop the flames from spreading.

The fire was under control by 7:45 a.m.

3 of 6 residences are damaged however hydro has been cut off to all 6 row houses for time being. <a href="https://twitter.com/hashtag/ottnews?src=hash">#ottnews</a> —@MessierOnFire

Investigations officer Marc Messier said in five families, four children and 16 adults, were forced out of their homes.

Three of them will be able to return in a few days when the heat and hydro is turned back on. The other two will have to wait until their damaged units are repaired, Messier said.

"The witness did mention he had been smoking and the way they explained that they were discarding their cigarettes gives us every reason to believe that this is what caused the fire," he said.