BRIDGEPORT, Conn. -- Officials deem a three-alarm fire at a vacant building in Bridgeport suspicious, Eyewitness News has learned.

"There's no way for the fire to have been accidental," Bridgeport Assistant Fire Chief Dominick Carfi told Eyewitness News. "We are calling the fire suspicious."

Firefighters received calls for the fire at the Remington Arms Plant at about 2 p.m. Within 45 minutes, fire officials called for a third alarm as the building's fourth floor was fully engulfed in flames, Carfi told Eyewitness News.

"We do have some flames in an area about a third of the way back into the structure," Carfi said at 5 p.m. "We have some firefighters on the floor, working on those hot spots."

Fire officials had concerns for firefighters' safety after floors inside the building collapsed and the roof caved in.

"Because of the complexity of the structure and the weak stability, we've had a difficult time getting firefighters in the area," Carfi said.

Channel 3 Eyewitness News reporter Leon Collins reported firefighters got the fire under control at about 5:30 p.m., but flames continued to burn inside the building through the 6 p.m. hour.

Authorities reported the fire was in the area of Helen and Maple streets, not far from Barnum Avenue. The fire was visible from Interstate 95 at exit 28, and police closed some streets in the area.

"There's no way for the fire to have been accidental. We are calling the fire suspicious." - Dominick Carfi Bridgeport Assistant Fire Chief

Fairfield fire officials have sent a ladder truck to the scene to assist Bridgeport crews. Carfi told Eyewitness News six engine companies and three ladder trucks responded to the scene. Collins reported an arson investigation squad has responded to the scene.

The building has remained vacant for 10 years and has no electrical or gas supply, but that hasn't kept people from entering.

"The building has been known to be occupied by vagrants at times and there have been people who break in for components and copper wire," Carfi said.

At least one firefighter who sustained a minor injury was hospitalized for observation.