NEW YORK (CBSNewYork) — At least two dozen families were picking up the pieces Sunday evening after an extra-alarm fire ripped through their Bronx apartment building and gutted the inside.

As CBS2’s Reena Roy reported, red hot flames and black smoke billowed through the sky as the fire engulfed the top floors of the 50-unit building – on Clay Avenue near 173rd Street in the Claremont section of the Bronx. The response level was raised to four alarms.

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“I took my dog and just ran out. It was very terrifying,” said resident Magali Negron. “There are a lot of kids in that building.”

Residents woke up to the chaos, forced to evacuate mid-sleep just after 5 a.m. They were woken up by firefighters knocking on doors, yelling for them to evacuate.

“We were looking outside because there was a, we heard glass breaking. Then when I went outside, all I smelled was fire. So then we ran downstairs and they told us to get out,” resident Valery Paredes said.

“I was asleep and when I woke up I heard the glass shattering, and then as I’m looking out my peephole, I saw the Fire Department in the hallway and they knocked on the door and told me we had to leave,” said Rosaria Rivera.

Many spent hours in the cold, wrapped in blankets as they watched their five-story building burn while speaking with the Red Cross.

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“That is crazy,” resident Rosaria Rivera said. “Now I have nothing. I don’t even know where to start from here.”

Fire officials said the blaze broke out on the top floor, spreading quickly. It took 400 firefighters more than two hours to get the fire under control, spraying water and breaking through the roof to contain it as fast as possible.

But the water damage was extensive. The top floors had been reduced to charred and burned walls, and the water damage affected the lower levels.

Several people suffered minor injuries. The FDNY says one civilian was transported to Bronx-Lebanon Hospital Center with minor injuries. Additionally, authorities say two firefighters were treated on scene for smoke inhalation.

“Very difficult fire. They made a very aggressive attack, but it was a rehab building where they had double ceilings on the top floor for firefighters to gain access to the cockloft, It requires a lot more,” said FDNY Deputy Assistant Chief Richard Howe. “You’re pulling down one ceiling, then the other, and the fire was quickly spreading in the cockloft area.”

There was a long way to go Sunday night to clean up the mess, with water still streaming out of the building. The inside of the building was severely gutted, and it was unclear late Sunday when the families would be able to move back in.

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The fire marshal late Sunday was investigating what sparked the blaze.