Rescuers said at least eight people remain beneath the debris.
Preliminary reports said the cause of the collapse might have been a breach of safety regulations at the construction site. A criminal case has been opened into the case, Baku Prosecutor Aziz Seidov said.
Azerbaijani media reported that two construction managers involved in the project have already been arrested.
A spokesman for the construction company said he heard the sound of an explosion before the building collapsed, but no eyewitnesses have confirmed this.
Other eyewitnesses said they felt a tremor before the building collapsed, but those reports have been dismissed by local officials.
Some officials suggested that those responsible for the tragedy deliberately spread rumors of a tremor as a way of avoiding responsibility.
Residents in nearby buildings were evacuated following reports that their homes could also be in danger of collapse.
Investigators said work at the site began five years ago, and that 16 floors had been built by the time of the collapse.
