Five people from separate units in the Altoona two-story duplex died in the blaze, Blair County Coroner Patricia Ross told The Associated Press. She declined to release further details about the victims pending notification of their families.
Three people escaped the fire and were being assisted by the Red Cross, the Altoona Mirror reported.
Altoona Fire Department Assistant Chief Tim Hileman told the newspaper that firefighters initially found two victims but after the flames were put out, another search yielded three more.
"It's going to be a few long hard days for the guys," Hileman told the Altoona Mirror, adding it was "a very tough situation" for the firefighters, some of whom went through three and four air-packs because they didn't want to stop searching for survivors in the burning, smoke-choked building.
WJAC-TV reported the fire broke out around 6:45 a.m., spewing flames visible across the city of about 45,000 people. Officials told the station no one on the second floor of the duplex made it out alive.
The station reported the fire was under control around 9:30 a.m. but the building was heavily damaged. A fire department official told WJAC-TV the building had smoke alarms.
A state police fire marshal was at the scene about 85 miles west of Harrisburg.
Information from: Altoona Mirror