The explosion Thursday in Wilhelmsburg, 30 miles west of Vienna, may have been caused by natural gas, authorities said.
During the night, about 200 firefighters, soldiers, police and dogs searched through the mound of rubble. One woman was brought out alive after medics amputated both her legs to free her.
Rescuers pulled the girl from the ruins after digging with their hands for more than two hours. After being taken to a hospital, she underwent surgery for her injuries and was in an intensive care unit this morning. Emergency workers said the girl was in good condition considering her ordeal.
Officials said it was unlikely that many more survivors would be found.
Â"This is a hopeless situation,Â" Erwin Proell, governor of Lower Austria state, said late Thursday. Â"There are practically no hollow pockets in the mound of rubble.Â"
Fire department chief Wilfried Weissgraeber told reporters that the blast on Thursday evening was heard three miles away.
Weissgraeber said a resident had noticed the smell of gas minutes before he left the building, narrowly escaping the blast.
It was unclear how many people were inside the building, which contained 12 apartments, at the time of the explosion.
Officials first estimated that 30 to 40 people may have been buried in the ruins, but Austrian television reported later that many of the residents had been out of the building at the time of the blast. Wilhelmsburg Mayor Otto Kernstock told the Austria Press Agency Friday that six were missing.
Proell said on state television that the explosion may have been caused by a hole accidentally drilled into a gas pipe during work to install at least one lightning rod.
After people noticed the odor of gas, they were ordered to leave the building, and a nearby kindergarten was evacuated. However, residents were allowed to return to their homes after repairs were made. The blast occurred about a half-hour later.
Meanwhile, many organizations, companies and private people offered money and apartments for those rendered homeless by the explosion.