The blaze quickly turned into an inferno, burning victims alive, while others leapt to safety, but many women workers were too scared to jump and were trapped.
Thirty-five women died, according to a forensics official.
Funerals of some of the victims took place on Sunday afternoon, attended by a king's chamberlain and four ministers.
Forensic examiners found another body on Sunday, bringing the death toll to at least 55, the official news agency MAP, said.
"The people who died were either asphyxiated or burned," said a firefighter.
Chakib Benmoussa, the interior minister, said an investigation into the cause of the blaze would also examine security measures and work conditions at the factory, MAP reported.
The minister said chemicals in the building sent the blaze out of control and delayed the rescue effort by hours.
Firefighters said many victims were trapped in the spiral stairwell of the building.
"It's a building with a ground floor and three upper floors specialising in making furniture, therefore there were highly inflammable products,"
Moustapha Taouil of the Casablanca civil protection service said.
"We confirmed during our examination that the owners of the premises failed to respect legal requirements for this kind of industry including staff training," he said.
More seriously, "the owner, in contravention of the law, locked staff inside the plant apparently to prevent theft of raw material. It was this that prevented them getting out."
Taouil said the fire had been started by a short circuit on the ground floor where power saws were located.
"The fire was caused by lack of proper maintenance of certain machines and electrical installations," he said.
"All the doors were blocked and nobody was able to escape through the exits," Smail Benhamed, 19, who jumped from the second floor, said.
Former employee Fadila Khadija, 28, alleged: "There was no emergency exit, the extinguishers were empty and the working conditions were difficult."
One security source said windows had been fitted with iron bars, making escape difficult.