The fire department was busy on Tuesday night cleaning up a diesel fuel spill that occurred on the roof of a downtown Calgary building.

They say that a company was installing a new generator and fuel was being transferred from one tank to another when a malfunction caused the diesel to spill onto the roof.

Initial reports say that hundreds of litres were released, but that number dropped to just under 50 litres when crews assessed the situation.

The fire department still had a challenge in cleaning up the mess. "We've drawn off as much of the product as we can with pumps. The roofing company will then remediate the roof," said Dist. Chief Larry Craig.

There were about 50 firefighters on scene for about two hours, Craig said, but that was a precaution to keep the residents of the building safe. "We're taking serious precautions for diesel fuel."

No one was injured in the incident as there was no one around when the spill occurred.

None of the fuel had seeped into the sewer system.