As many as two dozen firefighters were called in to battle a stubborn house fire in South Vancouver on Friday afternoon.

Flames could be seen shooting through the roof of the house near Fraser Street and 64th Avenue as crews sprayed foam onto the fire from the street.

Firefighters could not enter the building to battle the blaze because the house contains a marijuana grow-op.

Witness Gurpreet Dhillon told CTV News she was surprised to learn that there was a grow-op in the house. She said she hasn’t seen anyone in the building for quite a while.

When crews first arrived on scene, they found that the building was fortified, said Battalion Chief Ted Kadagies of Vancouver Fire and Rescue.

“They fought hard to get through that to get at the fire,” Kadagies said. “The fire gained a strong hold in the time it took to get into the bldg.”

The cause of the fire has not been determined.