The Vine Street fire started early on Tuesday morning.
Waterbury firefighters deemed a house fire on Vine Street as suspicious on Tuesday morning.
"Circumstances leading up to this is suspicious and certainly under investigation. I can't say for sure what happened, but a boarded-up home with this much of a head start,” Waterbury Deputy Fire Chief, David Stankus, said.
The two-alarm fire started around 1:30 a.m. add firefighters spent more than five hours extinguishing the suspicious overnight blaze at the vacant home.
"There was a lot of fire on all three floors, we were never able to make entry,” Stankus said.
At one point, the flames were so large that there was some concern that the fire could spread to two nearby vacant homes.
No injuries were reported. Investigators are looking into the cause of the blaze.
This is not the only fire in Waterbury to raise some concerns lately.
On April 7, 2012 firefighters battled one of the most intense fires in the city's history when an abandoned warehouse on Mill Street went up in flames.
On Tuesday morning, NBC Connecticut asked officials if they monitor abandoned buildings and homes in the city to help prevent suspicious fires like the one on Vine Street.
"There's a lot of vacant homes in the city and the mayor and the fire chief try to stay on top of it, so with blight ordinances and things of those sorts, it’s just a work in progress," said Stankus.