Winnipeg fire crews have extinguished a fire inside the basement of the former Canada Post building on Graham Avenue.

Firefighters were called to the downtown building, which is being renovated to become the Winnipeg Police Service's new headquarters, shortly after 1:30 p.m. CT.

Platoon chief Frank Leswick said the fire started in the ventilation system in the northeast corner of the basement.

"In a building this size, under construction, it was very, very tough," he told reporters.

"They were able to make their way into the basement in tough smoke conditions, and they found the fire in the ventilation system [and] they were able to extinguish it."

No one was injured. Fire officials did not have a damage estimate immediately available.

The building was evacuated and police were blocking off surrounding streets as firefighters went inside the building, but the area reopened to traffic at around 3 p.m.

Fire crews remain at the scene to ventilate the building.

This was the second fire at the construction site in recent months. A small fire was doused on the top floor on Aug. 3.