An early morning fire at a Canada Post building in the city's south end caused an estimated $1.5 million in damages, according to a fire official.  

Ottawa Fire Services was called to the fire at a four-storey office building at 720 Heron Rd. around 6:37 a.m. Saturday. The building is connected to Canada Post's head office campus on Riverside Drive. 

When firefighters arrived on scene they could see heavy black smoke billowing from the second floor on the east side of the building, Ottawa Fire Services said in a release. Flames were also visible on the first floor.

The heat from the flames was so intense it caused some windows to break.

The three-alarm fire was under control by around 7:20 a.m. No injuries were reported. 

Postal delivery not affected

A Canada Post spokesperson said in an email to CBC News the fire will not impact postal service and that the building was empty at the time of the fire, as it is primarily staffed during the week.

"As soon as it is safe to enter the building, we will assess the damage, begin the cleanup and put contingency plans in place for any employees that will have to be moved temporarily to another building on campus," Canada Post said.

The damage estimate from the fire was originally pegged at $500,000, but Ottawa Fire Services investigations officer Marc Messier tweeted later Saturday morning the estimate had risen by $1 million. The Fire Marshall is investigating. 

Most of the damage to the building is due to smoke. 

The cause of the fire is unknown.