Six manhole covers blew off Friday afternoon in Arbour Lake on Friday afternoon. ((Tara Weber/CBC))

Dozens of homes in Arbour Lake were evacuated Friday afternoon after an explosion blew manhole covers into the air.

"Several manhole covers had jumped off the ground, and there was a loud bang heard," said fire department spokesman Brian McAsey, who was on scene in the northwest Calgary neighbourhood.

Mcasey said the force of explosion was tremendous, causing six manholes to blow off.

Several blocks in the area around Arbour Lake Way N.W. and Arbour Lake Drive N.W. were evacuated just after 12 p.m. MT.

"Upon investigation we discovered that there was actually a product that went down a sanitary sewer and this product ignited and caused an explosion."

The Hazardous Materials Response team and police are analyzing the substance, said McAsey.

Video submitted by Kent and Lewis Noguchi, Arbour Lake residents.

Residents were allowed to return home after they checked in to the Arbour Lake Community Centre.

Some homes were minimally damaged by flooding. The explosion emptied pea traps – the curved part of the pipe under toilets.

Neighbours said they heard a big bang, and that there was black sludge in their sinks and toilets that smelled like gasoline.

No charges have been laid.