OTTAWA -- Ottawa fire investigators are searching through the rubble of a housing development in Kanata for the cause of a massive fire that destroyed 12 townhouse units that were under construction.

Damage is estimated at $6 million after the fire in the Connections in Kanata development by Mattamy Homes, near Canadian Tire Centre.

Ottawa fire received multiple 911 calls at 6:07 p.m. Wednesday reporting a fire in homes under construction on Culdaff Road, near Palladium Drive.

An Ottawa fire spokesperson said several callers reported smoke and flames in townhomes under construction, while some callers warned there were propane tanks inside the homes.

Only the skeletons of the homes were standing before the fire started, with no electricity connected to the building and no windows or doors installed.

"I mean it is a massive fire, it was just after the supper hour, around 6 o’clock you could start to hear in this neighbourhood sirens that were relentless, it was not stopping," said CTV Morning Live host Annette Goerner during an interview on CTV News at Six. "Curious neighbours by the hundreds started pouring out on to the streets."

The development has three blocks of 12 townhouses each, for a total of 36, three-storey townhouses. Ottawa Fire Public Information Officer Nicholas DeFazio told CTV News Ottawa that when firefighters arrived on scene, six of the units were fully engulfed in flames, and the fire was spreading into another block of six townhouses.

There were 10 fire trucks on the scene early Wednesday evening battling the fire.

"It's a major attack by firefighters trying to get this under control," said Goerner. "Flames were completely engulfing the entire structure."

DeFazio says firefighters were able to prevent the fire from spreading to 24 townhouses. Crews were also able to cool propane tanks located outside the development and prevented them from catching on fire.

One firefighter was treated by paramedics on the scene for heat exhaustion.

Smoke could be seen as far away as Westboro and Barrhaven, and across the river in western Quebec.

The fire was located inside the Connections in Kanata development by Mattamy Homes. It includes townhomes and singles.

"Find fun and family recreation in every season at Connections in Kanata, inspired living made easy," says Mattamy Homes on its website.

Mattamy Homes said Thursday afternoon that it was in the process of informing its customers about the fire.

"We can confirm that a fire broke out at a block of 12 homes in Mattamy's Connections community in Kanata on October 6. These homes are all currently under construction and none are occupied," said Mattamy Homes in a statement to CTV News Ottawa.

"No Mattamy or trade workers are believed to have been present at the time of the fire. We are thankful that there were no injuries and that the fire did not spread beyond the particular block. We are cooperating fully with the relevant authorities, who are leading the investigation at this time."

The cause of the fire is under investigation.