Responding to a one-alarm fire, the Boston Fire Department quickly contained a large blaze Monday night at 182 Beacon St. in Back Bay. No injuries were reported, but the property suffered extensive damage, according to Boston authorities.

At about 6 p.m. BFD responded to a call that the back of the roof of a six-story, 14-unit condominium building was on fire said BFD spokesman Steve MacDonald.

“The roof deck was on fire. It was pretty spectacular. We got a lot of phone calls on it,” he said. “The fire was confined to the roof, however, it did drop down to the top floor into the condo that’s on the sixth floor and we have water damage throughout all the stairways and common landings on each floor.”

The Fire Department estimated the damage to be about $1 million, according to the BFD Twitter page. MacDonald said investigators are still seeking how and where the fire started, but significant water damge has been done.

“There is extensive water damage throughout the building, so it went down all the common areas,” he said. “A week or two weeks from now we will start seeing the swelling of floors and ceilings saturated with water and in danger of collapsing.”

MacDonald said several people would be displaced as a result of the fire.

“It still remains to be seen if they will need a place to stay, to be put up in a hotel or with family or friends,” he said. “It will be up to them. We [BFD], along with the mayor’s office and [BFD Victim’s Assistance] people will talk to them and see if they need the Red Cross to help them.”

Cameron Guilmette, 23, a retail worker and resident of the top floor of 182 Beacon St., said he witnessed the fire firsthand.

“There were flames everywhere and I ran downstairs to grab a fire extinguisher from the unit and came back up,” he said. “It had little effect and by the time I got to the second [extinguisher] unit, the flames engulfed the back part and were moving toward the riverside.”

Guilmette said he ran downstairs, pulled the fire alarm, grabbed some belongings from his unit and exited the building.

Gabrielle Cossolini, 23, a lawyer and neighbor to the condominium, said she could see a large black cloud of smoke coming from the back of the building.

“I had just got home from work and I was sitting having dinner and some man buzzed everyone and told them to run out because there was a fire,” she said. “We came out and there was a huge crowd and some smoke back there.”

Annie Phelan, 28, a resident of 186 Beacon St., said she saw large flames that quickly unnerved her.

“I was sitting at my window drawing, and all of a sudden I started seeing all this smoke,” she said. “I looked out the window and I saw flames coming from the top of the building, so I grabbed my dog and ran down the stairs.”

Stephanie Giunta, a sophomore at Fisher College studying communications, said she heard about the fire from social media.

“As soon as I got here, they [BFD] were putting up more ladders and bringing up the axes and stuff, but I saw the pictures on Twitter and it looked like it was a huge fire,” she said.

Giunta said she heard the sirens from the fire trucks and saw the Boston Police Department starting to shut down the street.

“I got excited so I ran right toward it, but a lot of people seemed freaked out by it,” she said. “I really hope everyone will be okay.”