An early morning Bronx fire that injured at least six now has firefighters investigating what started the four-alarm blaze.

Flames erupted from the building at 1893 Andrews Ave. in Morris Heights around 2:30 a.m. Tuesday, NY1 reported. Officials believe the fire started in a fifth floor apartment.

“It started to get cloudy and as we went down the stairs. We were looking for my little sister. We found her — she ended up being downstairs,” resident Ronnie Dukes said to CBS. “Honestly, it was a hectic time as anybody would expect.”

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Five residents and one firefighter were injured in the blaze, ABC added in a related report. However, none of the injuries were life-threatening.

Officials told CBS that the fire spread quickly from apartment to apartment, forcing the evacuation of hundreds of residents and gutting the entire fifth floor.

"All the apartments on the top floor sustained severe fire damage," FDNY Chief Jay Jonas said to ABC.

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The cause of the fire remains under investigation, according to NY1, which added that the Red Cross is now working with approximately 10 families who were displaced by the fire.