Firefighters said flames broke out in the home on Riverside Avenue in Seaford at around 6:15 a.m.
Officials said the fire spread quickly, engulfing the entire home before firefighters arrived.
Two chiefs from the Wantagh Fire Department rushed inside the burning home to try to rescue the residents.
One of them was burned and was taken to Nassau University Medical Center in East Meadow for treatment.
An 80-year-old woman was pronounced dead at the scene.
Her 60-year-old daughter was treated at a hospital for smoke inhalation.
Officials say as many as five people lived in the home.
The cause of the fire is under investigation.
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