Ms Shabazz suffered third-degree burns over 80 per cent of her body, said police.
She was listed in critical condition at Jacobi Hospital in the New York borough of the Bronx, said a nursing supervisor, Pat Strauss. "It does not look good for her," a police spokesman, Detective Sergeant William Rinaldi, said.
Her apartment was not destroyed by the fire, "just the areas surrounding her", Det Sgt Rinaldi said. Police were investigating the fire as a crime.
He wouldn't comment on whether anyone else was in the apartment at the time of the fire.
Malcolm X was the voice of Black Muslims in America during the early 1960s. His raw talk about race jolted Americans, and his black nationalist appeal contrasted with the growing and integrated civil rights movement.
He was assassinated in February 1965. For 30 years, there was a rift between Ms Shabazz and Nation of Islam leader Louis Farrakhan, whom Shabazz believed had played a role in her husband's death.
The two publicly reconciled in 1995.
Malcolm X criticised Nation of Islam founder Elijah Muhammad shortly before his death and was labeled a traitor by Mr Farrakhan.Reuse content