An early morning apartment fire killed an 81-year-old woman in Prospect Lefferts Gardens.

The fire broke out just before 1 a.m. Friday on the fourth floor of a residential building at 35 Winthrop St.

Firefighters battled the blaze in below-freezing conditions.

Authorities said the unidentified woman was found unconscious and unresponsive inside the apartment and was pronounced dead at the scene.

A neighbor said the apartment where the fire started was known to have clutter inside. He said he noticed what he described as an electrical smoke smell and called 911.

“I shut my door immediately, and within ten minutes when I opened it, I couldn’t see out my door,” the neighbor said. “Other neighbors on the sixth floor said the same thing. There was a lot of adrenaline, trying to stay calm.”

A medical examiner will determine the woman’s cause of death.