By The Associated Press

INDIANAPOLIS — An estimated 100 animals died when an overnight fire filled an Indianapolis pet store with thick smoke and deadly gases, fire officials said.

It took firefighters about an hour to extinguish the blaze at Uncle Bill's Pet Center on Monday night because they had difficulty accessing the fire in the building's back roof area, the Indianapolis Fire Department said.

After dousing flames that had filled the building with thick, black smoke, crews discovered “what can only be described as a horrible tragedy" inside, with about 40 dogs, 25 parakeets, rabbits and other animals dead from smoke inhalation, Battalion Chief Rita Reith said in a news release.

“The animals were still in their respective cages and simply succumbed to the deadly gases produced by the smoke," Reith wrote.

Multiple reptiles, fish, an office cat and “a resilient guinea pig” that survived the fire were removed from the building and were being evaluated by pet store staff.

The cause of the fire remains under investigation.