After more than four hours of delicate work, firefighters freed the man, using large jacks to lift a concrete slab that had collapsed. But his fiancee was burned badly and died before rescuers could reach her, officials said.
The man was hospitalized in critical but stable condition with numerous injuries. Neither his name nor his fiancee's were immediately released.
Five children and two adults also were hurt, officials said, but none of the injuries was life-threatening. Survivors crawled through fire and debris to get to the street to safety.
Fire officials said they suspected natural gas was behind the blast, but the cause was still under investigation.
Firefighters were called about 3:45 a.m. Tuesday after a fireball erupted at Gate City Apartments, a few miles from downtown Birmingham. Photos taken by residents showed flames that turned the night sky bright orange.
The blast leveled about half the building, which burned before crews could get close enough to begin rescue work.
Battalion Chief C.W. Mardis of the Birmingham Fire and Rescue Service said the couple, in a first-floor apartment, apparently was asleep in bed at the time of the explosion, which blew out the exterior walls and caused the building collapse.
"The actual concrete slab from the second floor was on them," said Mardis.
Carefully, fire crews cleared away loose rubble to get to the remainder of the bedroom, where the two were trapped under the slab, he said.
"We were able to use hydraulic jacks and lifting blocks to lift it enough to get them out," Mardis said.
The man was badly injured and in critical condition by the time firefighters reached him, Mardis said, and the woman died before rescuers reached her.
Workers from Alagasco, the utility that provides natural gas in the area, were at the apartment complex after the explosion.
The apartment building will have to be demolished because the remaining section was unstable, Mardis said.