An early morning fire has caused more than $500,000 in damages to a Canada Post building on Heron Road. 

Ottawa Fire says the blaze broke out around 6:37 Saturday morning. 

When firefighters arrived flames were visible on the first story and smoke was visible on the second to the fourth storey of the commercial building. Ottawa Fire says the fire was so hot a number of broken windows were reported. 

According to Canada Post, the blaze happened in an office building that is part of the company's head office campus on Riverside Drive. The building is primarily used during the week and not on weekends. As such, nobody was inside the building at the time of the fire. 

"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," said Phil Legault, Canada Post media relations in a statement. 

Canada Post says the fire will not impact postal service.

Damages are estimated at more than $500,000.

A cause has yet to be determined.