The latest reports say at least six construction workers died in the building collapse. Earlier officials had said that seven people had died. The rescue operation is continuing.
Azerbaijani Prosecutor General Zakir Garalov said at least 26 workers are still trapped under the rubble, adding that there could be more people missing.
Preliminary reports said the cause of the collapse could have been breaches in safety regulations at the construction site. A criminal case has been opened, Baku Prosecutor Aziz Seidov said earlier.
Police have already arrested the CEO of the construction company, Ali Muradov, and his brother, as well as two construction managers.
A spokesman for the construction company said he heard the sound of an explosion before the building collapsed, but no witnesses have confirmed this.
Other eyewitnesses said they had felt a tremor before the building collapsed, but these reports have been rejected by local officials. Some officials suggested that those responsible for the tragedy had deliberately spread rumors of a tremor as a means of averting responsibility.
Residents living in nearby apartment blocks have been evacuated, following reports that their buildings may also be under threat.
Investigators said building work at the site started five years ago, and 16 floors had been built at the time of the collapse.